From 08e1d8ece4314b56d64fa08595c2e043b97896d1 Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Mon, 6 Apr 2020 17:19:31 +0100
Subject: Split off operations from main expr enum

---
 dhall/src/semantics/resolve/resolve.rs | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

(limited to 'dhall/src/semantics/resolve')

diff --git a/dhall/src/semantics/resolve/resolve.rs b/dhall/src/semantics/resolve/resolve.rs
index 6e50fa6..3e0022f 100644
--- a/dhall/src/semantics/resolve/resolve.rs
+++ b/dhall/src/semantics/resolve/resolve.rs
@@ -11,7 +11,7 @@ use crate::syntax;
 use crate::syntax::map::DupTreeMap;
 use crate::syntax::{
     BinOp, Builtin, Expr, ExprKind, FilePath, FilePrefix, Hash, ImportMode,
-    ImportTarget, Span, UnspannedExpr, URL,
+    ImportTarget, OpKind, Span, UnspannedExpr, URL,
 };
 use crate::{Parsed, Resolved};
 
@@ -179,12 +179,13 @@ impl ImportLocation {
         };
 
         let asloc_ty = make_aslocation_uniontype();
-        let expr = mkexpr(ExprKind::Field(asloc_ty, field_name.into()));
+        let expr =
+            mkexpr(ExprKind::Op(OpKind::Field(asloc_ty, field_name.into())));
         match arg {
-            Some(arg) => mkexpr(ExprKind::App(
+            Some(arg) => mkexpr(ExprKind::Op(OpKind::App(
                 expr,
                 mkexpr(ExprKind::TextLit(arg.into())),
-            )),
+            ))),
             None => expr,
         }
     }
@@ -261,21 +262,21 @@ fn resolve_one_import(
 /// Desugar the first level of the expression.
 fn desugar(expr: &Expr) -> Cow<'_, Expr> {
     match expr.kind() {
-        ExprKind::Completion(ty, compl) => {
+        ExprKind::Op(OpKind::Completion(ty, compl)) => {
             let ty_field_default = Expr::new(
-                ExprKind::Field(ty.clone(), "default".into()),
+                ExprKind::Op(OpKind::Field(ty.clone(), "default".into())),
                 expr.span(),
             );
             let merged = Expr::new(
-                ExprKind::BinOp(
+                ExprKind::Op(OpKind::BinOp(
                     BinOp::RightBiasedRecordMerge,
                     ty_field_default,
                     compl.clone(),
-                ),
+                )),
                 expr.span(),
             );
             let ty_field_type = Expr::new(
-                ExprKind::Field(ty.clone(), "Type".into()),
+                ExprKind::Op(OpKind::Field(ty.clone(), "Type".into())),
                 expr.span(),
             );
             Cow::Owned(Expr::new(
@@ -304,7 +305,7 @@ fn traverse_resolve_expr(
                     .format(),
             )?,
         },
-        ExprKind::BinOp(BinOp::ImportAlt, l, r) => {
+        ExprKind::Op(OpKind::BinOp(BinOp::ImportAlt, l, r)) => {
             match traverse_resolve_expr(name_env, l, f) {
                 Ok(l) => l,
                 Err(_) => {
-- 
cgit v1.3.1


From fff4c46e09d4edf25eba737f4d71bfdb1dbf4a82 Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Mon, 6 Apr 2020 22:11:54 +0100
Subject: Extract operation-related code to a new module

---
 dhall/src/lib.rs                       |   1 +
 dhall/src/operations.rs                | 865 +++++++++++++++++++++++++++++++++
 dhall/src/semantics/builtins.rs        |   5 +-
 dhall/src/semantics/nze/nir.rs         |   3 +-
 dhall/src/semantics/nze/normalize.rs   | 301 +-----------
 dhall/src/semantics/resolve/resolve.rs |   3 +-
 dhall/src/semantics/tck/typecheck.rs   | 515 +-------------------
 dhall/src/syntax/ast/expr.rs           |  65 +--
 dhall/src/syntax/binary/decode.rs      |   3 +-
 dhall/src/syntax/binary/encode.rs      |   5 +-
 dhall/src/syntax/text/parser.rs        |   2 +-
 dhall/src/syntax/text/printer.rs       |  11 +-
 serde_dhall/src/value.rs               |   3 +-
 13 files changed, 900 insertions(+), 882 deletions(-)
 create mode 100644 dhall/src/operations.rs

(limited to 'dhall/src/semantics/resolve')

diff --git a/dhall/src/lib.rs b/dhall/src/lib.rs
index 98ad4f0..e00177c 100644
--- a/dhall/src/lib.rs
+++ b/dhall/src/lib.rs
@@ -11,6 +11,7 @@
 mod tests;
 
 pub mod error;
+pub mod operations;
 pub mod semantics;
 pub mod syntax;
 
diff --git a/dhall/src/operations.rs b/dhall/src/operations.rs
new file mode 100644
index 0000000..363cd10
--- /dev/null
+++ b/dhall/src/operations.rs
@@ -0,0 +1,865 @@
+use itertools::Itertools;
+use std::borrow::Cow;
+use std::cmp::max;
+use std::collections::HashMap;
+
+use crate::error::{ErrorBuilder, TypeError};
+use crate::semantics::{
+    merge_maps, mk_span_err, mkerr, ret_kind, ret_op, ret_ref, Binder, Closure,
+    Hir, HirKind, Nir, NirKind, Ret, TextLit, Tir, TyEnv, Type,
+};
+use crate::syntax::map::DupTreeSet;
+use crate::syntax::{
+    trivial_result, BinOp, Builtin, Const, ExprKind, Label, NumKind, Span,
+};
+
+/// Operations
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum OpKind<SubExpr> {
+    ///  `f a`
+    App(SubExpr, SubExpr),
+    /// Binary operations
+    BinOp(BinOp, SubExpr, SubExpr),
+    ///  `if x then y else z`
+    BoolIf(SubExpr, SubExpr, SubExpr),
+    ///  `merge x y : t`
+    Merge(SubExpr, SubExpr, Option<SubExpr>),
+    ///  `toMap x : t`
+    ToMap(SubExpr, Option<SubExpr>),
+    ///  `e.x`
+    Field(SubExpr, Label),
+    ///  `e.{ x, y, z }`
+    Projection(SubExpr, DupTreeSet<Label>),
+    ///  `e.(t)`
+    ProjectionByExpr(SubExpr, SubExpr),
+    ///  `x::y`
+    Completion(SubExpr, SubExpr),
+}
+
+impl<SE> OpKind<SE> {
+    pub fn traverse_ref<'a, SE2, Err>(
+        &'a self,
+        mut f: impl FnMut(&'a SE) -> Result<SE2, Err>,
+    ) -> Result<OpKind<SE2>, Err> {
+        // Can't use closures because of borrowing rules
+        macro_rules! expr {
+            ($e:expr) => {
+                f($e)?
+            };
+        }
+        macro_rules! opt {
+            ($e:expr) => {
+                $e.as_ref().map(|e| Ok(expr!(e))).transpose()?
+            };
+        }
+
+        use OpKind::*;
+        Ok(match self {
+            App(f, a) => App(expr!(f), expr!(a)),
+            BinOp(o, x, y) => BinOp(*o, expr!(x), expr!(y)),
+            BoolIf(b, t, f) => BoolIf(expr!(b), expr!(t), expr!(f)),
+            Merge(x, y, t) => Merge(expr!(x), expr!(y), opt!(t)),
+            ToMap(x, t) => ToMap(expr!(x), opt!(t)),
+            Field(e, l) => Field(expr!(e), l.clone()),
+            Projection(e, ls) => Projection(expr!(e), ls.clone()),
+            ProjectionByExpr(e, x) => ProjectionByExpr(expr!(e), expr!(x)),
+            Completion(e, x) => Completion(expr!(e), expr!(x)),
+        })
+    }
+
+    pub fn map_ref<'a, SE2>(
+        &'a self,
+        mut f: impl FnMut(&'a SE) -> SE2,
+    ) -> OpKind<SE2> {
+        trivial_result(self.traverse_ref(|x| Ok(f(x))))
+    }
+}
+
+fn check_rectymerge(
+    span: &Span,
+    env: &TyEnv,
+    x: Nir,
+    y: Nir,
+) -> Result<(), TypeError> {
+    let kts_x = match x.kind() {
+        NirKind::RecordType(kts) => kts,
+        _ => {
+            return mk_span_err(
+                span.clone(),
+                "RecordTypeMergeRequiresRecordType",
+            )
+        }
+    };
+    let kts_y = match y.kind() {
+        NirKind::RecordType(kts) => kts,
+        _ => {
+            return mk_span_err(
+                span.clone(),
+                "RecordTypeMergeRequiresRecordType",
+            )
+        }
+    };
+    for (k, tx) in kts_x {
+        if let Some(ty) = kts_y.get(k) {
+            // TODO: store Type in RecordType ?
+            check_rectymerge(span, env, tx.clone(), ty.clone())?;
+        }
+    }
+    Ok(())
+}
+
+fn typecheck_binop(
+    env: &TyEnv,
+    span: Span,
+    op: BinOp,
+    l: &Tir<'_>,
+    r: &Tir<'_>,
+) -> Result<Type, TypeError> {
+    let span_err = |msg: &str| mk_span_err(span.clone(), msg);
+    use BinOp::*;
+    use NirKind::{ListType, RecordType};
+
+    Ok(match op {
+        RightBiasedRecordMerge => {
+            let x_type = l.ty();
+            let y_type = r.ty();
+
+            // Extract the LHS record type
+            let kts_x = match x_type.kind() {
+                RecordType(kts) => kts,
+                _ => return span_err("MustCombineRecord"),
+            };
+            // Extract the RHS record type
+            let kts_y = match y_type.kind() {
+                RecordType(kts) => kts,
+                _ => return span_err("MustCombineRecord"),
+            };
+
+            // Union the two records, prefering
+            // the values found in the RHS.
+            let kts = merge_maps(kts_x, kts_y, |_, _, r_t| r_t.clone());
+
+            let u = max(l.ty().ty(), r.ty().ty());
+            Nir::from_kind(RecordType(kts)).to_type(u)
+        }
+        RecursiveRecordMerge => {
+            check_rectymerge(&span, env, l.ty().to_nir(), r.ty().to_nir())?;
+
+            let hir = Hir::new(
+                HirKind::Expr(ExprKind::Op(OpKind::BinOp(
+                    RecursiveRecordTypeMerge,
+                    l.ty().to_hir(env.as_varenv()),
+                    r.ty().to_hir(env.as_varenv()),
+                ))),
+                span.clone(),
+            );
+            let x_u = l.ty().ty();
+            let y_u = r.ty().ty();
+            Type::new(hir.eval(env), max(x_u, y_u))
+        }
+        RecursiveRecordTypeMerge => {
+            check_rectymerge(&span, env, l.eval(env), r.eval(env))?;
+
+            // A RecordType's type is always a const
+            let xk = l.ty().as_const().unwrap();
+            let yk = r.ty().as_const().unwrap();
+            Type::from_const(max(xk, yk))
+        }
+        ListAppend => {
+            match l.ty().kind() {
+                ListType(..) => {}
+                _ => return span_err("BinOpTypeMismatch"),
+            }
+
+            if l.ty() != r.ty() {
+                return span_err("BinOpTypeMismatch");
+            }
+
+            l.ty().clone()
+        }
+        Equivalence => {
+            if l.ty() != r.ty() {
+                return span_err("EquivalenceTypeMismatch");
+            }
+            if l.ty().ty().as_const() != Some(Const::Type) {
+                return span_err("EquivalenceArgumentsMustBeTerms");
+            }
+
+            Type::from_const(Const::Type)
+        }
+        op => {
+            let t = Type::from_builtin(match op {
+                BoolAnd | BoolOr | BoolEQ | BoolNE => Builtin::Bool,
+                NaturalPlus | NaturalTimes => Builtin::Natural,
+                TextAppend => Builtin::Text,
+                ListAppend
+                | RightBiasedRecordMerge
+                | RecursiveRecordMerge
+                | RecursiveRecordTypeMerge
+                | Equivalence => unreachable!(),
+                ImportAlt => unreachable!("ImportAlt leftover in tck"),
+            });
+
+            if *l.ty() != t {
+                return span_err("BinOpTypeMismatch");
+            }
+
+            if *r.ty() != t {
+                return span_err("BinOpTypeMismatch");
+            }
+
+            t
+        }
+    })
+}
+
+fn typecheck_merge(
+    env: &TyEnv,
+    span: Span,
+    record: &Tir<'_>,
+    scrut: &Tir<'_>,
+    type_annot: Option<&Tir<'_>>,
+) -> Result<Type, TypeError> {
+    let span_err = |msg: &str| mk_span_err(span.clone(), msg);
+    use NirKind::{OptionalType, PiClosure, RecordType, UnionType};
+
+    let record_type = record.ty();
+    let handlers = match record_type.kind() {
+        RecordType(kts) => kts,
+        _ => return span_err("Merge1ArgMustBeRecord"),
+    };
+
+    let scrut_type = scrut.ty();
+    let variants = match scrut_type.kind() {
+        UnionType(kts) => Cow::Borrowed(kts),
+        OptionalType(ty) => {
+            let mut kts = HashMap::new();
+            kts.insert("None".into(), None);
+            kts.insert("Some".into(), Some(ty.clone()));
+            Cow::Owned(kts)
+        }
+        _ => return span_err("Merge2ArgMustBeUnionOrOptional"),
+    };
+
+    let mut inferred_type = None;
+    for (x, handler_type) in handlers {
+        let handler_return_type: Type = match variants.get(x) {
+            // Union alternative with type
+            Some(Some(variant_type)) => match handler_type.kind() {
+                PiClosure { closure, annot, .. } => {
+                    if variant_type != annot {
+                        return mkerr(
+                            ErrorBuilder::new(format!(
+                                "Wrong handler input type"
+                            ))
+                            .span_err(
+                                span,
+                                format!("in this merge expression",),
+                            )
+                            .span_err(
+                                record.span(),
+                                format!(
+                                    "the handler for `{}` expects a value of \
+                                     type: `{}`",
+                                    x,
+                                    annot.to_expr_tyenv(env)
+                                ),
+                            )
+                            .span_err(
+                                scrut.span(),
+                                format!(
+                                    "but the corresponding variant has type: \
+                                     `{}`",
+                                    variant_type.to_expr_tyenv(env)
+                                ),
+                            )
+                            .format(),
+                        );
+                    }
+
+                    // TODO: this actually doesn't check anything yet
+                    match closure.remove_binder() {
+                        Ok(v) => Type::new_infer_universe(env, v.clone())?,
+                        Err(()) => {
+                            return span_err("MergeReturnTypeIsDependent")
+                        }
+                    }
+                }
+                _ => {
+                    return mkerr(
+                        ErrorBuilder::new(format!(
+                            "merge handler is not a function"
+                        ))
+                        .span_err(span, format!("in this merge expression"))
+                        .span_err(
+                            record.span(),
+                            format!(
+                                "the handler for `{}` has type: `{}`",
+                                x,
+                                handler_type.to_expr_tyenv(env)
+                            ),
+                        )
+                        .span_help(
+                            scrut.span(),
+                            format!(
+                                "the corresponding variant has type: `{}`",
+                                variant_type.to_expr_tyenv(env)
+                            ),
+                        )
+                        .help(format!(
+                            "a handler for this variant must be a function \
+                             that takes an input of type: `{}`",
+                            variant_type.to_expr_tyenv(env)
+                        ))
+                        .format(),
+                    )
+                }
+            },
+            // Union alternative without type
+            Some(None) => Type::new_infer_universe(env, handler_type.clone())?,
+            None => return span_err("MergeHandlerMissingVariant"),
+        };
+        match &inferred_type {
+            None => inferred_type = Some(handler_return_type),
+            Some(t) => {
+                if t != &handler_return_type {
+                    return span_err("MergeHandlerTypeMismatch");
+                }
+            }
+        }
+    }
+    for x in variants.keys() {
+        if !handlers.contains_key(x) {
+            return span_err("MergeVariantMissingHandler");
+        }
+    }
+
+    let type_annot = type_annot
+        .as_ref()
+        .map(|t| t.eval_to_type(env))
+        .transpose()?;
+    Ok(match (inferred_type, type_annot) {
+        (Some(t1), Some(t2)) => {
+            if t1 != t2 {
+                return span_err("MergeAnnotMismatch");
+            }
+            t1
+        }
+        (Some(t), None) => t,
+        (None, Some(t)) => t,
+        (None, None) => return span_err("MergeEmptyNeedsAnnotation"),
+    })
+}
+
+pub fn typecheck_operation(
+    env: &TyEnv,
+    span: Span,
+    opkind: &OpKind<Tir<'_>>,
+) -> Result<Type, TypeError> {
+    let span_err = |msg: &str| mk_span_err(span.clone(), msg);
+    use NirKind::{ListType, PiClosure, RecordType, UnionType};
+    use OpKind::*;
+
+    Ok(match opkind {
+        App(f, arg) => {
+            match f.ty().kind() {
+                // TODO: store Type in closure
+                PiClosure { annot, closure, .. } => {
+                    if arg.ty().as_nir() != annot {
+                        return mkerr(
+                            ErrorBuilder::new(format!(
+                                "wrong type of function argument"
+                            ))
+                            .span_err(
+                                f.span(),
+                                format!(
+                                    "this expects an argument of type: {}",
+                                    annot.to_expr_tyenv(env),
+                                ),
+                            )
+                            .span_err(
+                                arg.span(),
+                                format!(
+                                    "but this has type: {}",
+                                    arg.ty().to_expr_tyenv(env),
+                                ),
+                            )
+                            .note(format!(
+                                "expected type `{}`\n   found type `{}`",
+                                annot.to_expr_tyenv(env),
+                                arg.ty().to_expr_tyenv(env),
+                            ))
+                            .format(),
+                        );
+                    }
+
+                    let arg_nf = arg.eval(env);
+                    Type::new_infer_universe(env, closure.apply(arg_nf))?
+                }
+                _ => return mkerr(
+                    ErrorBuilder::new(format!(
+                        "expected function, found `{}`",
+                        f.ty().to_expr_tyenv(env)
+                    ))
+                    .span_err(
+                        f.span(),
+                        format!("function application requires a function",),
+                    )
+                    .format(),
+                ),
+            }
+        }
+        BinOp(o, l, r) => typecheck_binop(env, span, *o, l, r)?,
+        BoolIf(x, y, z) => {
+            if *x.ty().kind() != NirKind::from_builtin(Builtin::Bool) {
+                return span_err("InvalidPredicate");
+            }
+            if y.ty().ty().as_const() != Some(Const::Type) {
+                return span_err("IfBranchMustBeTerm");
+            }
+            if y.ty() != z.ty() {
+                return span_err("IfBranchMismatch");
+            }
+
+            y.ty().clone()
+        }
+        Merge(record, scrut, type_annot) => {
+            typecheck_merge(env, span, record, scrut, type_annot.as_ref())?
+        }
+        ToMap(record, annot) => {
+            if record.ty().ty().as_const() != Some(Const::Type) {
+                return span_err("`toMap` only accepts records of type `Type`");
+            }
+            let record_t = record.ty();
+            let kts = match record_t.kind() {
+                RecordType(kts) => kts,
+                _ => {
+                    return span_err("The argument to `toMap` must be a record")
+                }
+            };
+
+            if kts.is_empty() {
+                let annot = if let Some(annot) = annot {
+                    annot
+                } else {
+                    return span_err(
+                        "`toMap` applied to an empty record requires a type \
+                         annotation",
+                    );
+                };
+                let annot_val = annot.eval_to_type(env)?;
+
+                let err_msg = "The type of `toMap x` must be of the form \
+                               `List { mapKey : Text, mapValue : T }`";
+                let arg = match annot_val.kind() {
+                    ListType(t) => t,
+                    _ => return span_err(err_msg),
+                };
+                let kts = match arg.kind() {
+                    RecordType(kts) => kts,
+                    _ => return span_err(err_msg),
+                };
+                if kts.len() != 2 {
+                    return span_err(err_msg);
+                }
+                match kts.get(&"mapKey".into()) {
+                    Some(t) if *t == Nir::from_builtin(Builtin::Text) => {}
+                    _ => return span_err(err_msg),
+                }
+                match kts.get(&"mapValue".into()) {
+                    Some(_) => {}
+                    None => return span_err(err_msg),
+                }
+                annot_val
+            } else {
+                let entry_type = kts.iter().next().unwrap().1.clone();
+                for (_, t) in kts.iter() {
+                    if *t != entry_type {
+                        return span_err(
+                            "Every field of the record must have the same type",
+                        );
+                    }
+                }
+
+                let mut kts = HashMap::new();
+                kts.insert("mapKey".into(), Nir::from_builtin(Builtin::Text));
+                kts.insert("mapValue".into(), entry_type);
+                let output_type: Type = Nir::from_builtin(Builtin::List)
+                    .app(Nir::from_kind(RecordType(kts)))
+                    .to_type(Const::Type);
+                if let Some(annot) = annot {
+                    let annot_val = annot.eval_to_type(env)?;
+                    if output_type != annot_val {
+                        return span_err("Annotation mismatch");
+                    }
+                }
+                output_type
+            }
+        }
+        Field(scrut, x) => {
+            match scrut.ty().kind() {
+                RecordType(kts) => match kts.get(&x) {
+                    Some(val) => Type::new_infer_universe(env, val.clone())?,
+                    None => return span_err("MissingRecordField"),
+                },
+                NirKind::Const(_) => {
+                    let scrut = scrut.eval_to_type(env)?;
+                    match scrut.kind() {
+                        UnionType(kts) => match kts.get(x) {
+                            // Constructor has type T -> < x: T, ... >
+                            Some(Some(ty)) => Nir::from_kind(PiClosure {
+                                binder: Binder::new(x.clone()),
+                                annot: ty.clone(),
+                                closure: Closure::new_constant(scrut.to_nir()),
+                            })
+                            .to_type(scrut.ty()),
+                            Some(None) => scrut,
+                            None => return span_err("MissingUnionField"),
+                        },
+                        _ => return span_err("NotARecord"),
+                    }
+                }
+                _ => return span_err("NotARecord"),
+            }
+        }
+        Projection(record, labels) => {
+            let record_type = record.ty();
+            let kts = match record_type.kind() {
+                RecordType(kts) => kts,
+                _ => return span_err("ProjectionMustBeRecord"),
+            };
+
+            let mut new_kts = HashMap::new();
+            for l in labels {
+                match kts.get(l) {
+                    None => return span_err("ProjectionMissingEntry"),
+                    Some(t) => {
+                        use std::collections::hash_map::Entry;
+                        match new_kts.entry(l.clone()) {
+                            Entry::Occupied(_) => {
+                                return span_err("ProjectionDuplicateField")
+                            }
+                            Entry::Vacant(e) => e.insert(t.clone()),
+                        }
+                    }
+                };
+            }
+
+            Type::new_infer_universe(env, Nir::from_kind(RecordType(new_kts)))?
+        }
+        ProjectionByExpr(record, selection) => {
+            let record_type = record.ty();
+            let rec_kts = match record_type.kind() {
+                RecordType(kts) => kts,
+                _ => return span_err("ProjectionMustBeRecord"),
+            };
+
+            let selection_val = selection.eval_to_type(env)?;
+            let sel_kts = match selection_val.kind() {
+                RecordType(kts) => kts,
+                _ => return span_err("ProjectionByExprTakesRecordType"),
+            };
+
+            for (l, sel_ty) in sel_kts {
+                match rec_kts.get(l) {
+                    Some(rec_ty) => {
+                        if rec_ty != sel_ty {
+                            return span_err("ProjectionWrongType");
+                        }
+                    }
+                    None => return span_err("ProjectionMissingEntry"),
+                }
+            }
+
+            selection_val
+        }
+        Completion(..) => {
+            unreachable!("This case should have been handled in resolution")
+        }
+    })
+}
+
+fn normalize_binop(o: BinOp, x: &Nir, y: &Nir) -> Ret {
+    use BinOp::*;
+    use NirKind::{EmptyListLit, NEListLit, Num, RecordLit, RecordType};
+    use NumKind::{Bool, Natural};
+
+    match (o, x.kind(), y.kind()) {
+        (BoolAnd, Num(Bool(true)), _) => ret_ref(y),
+        (BoolAnd, _, Num(Bool(true))) => ret_ref(x),
+        (BoolAnd, Num(Bool(false)), _) => ret_kind(Num(Bool(false))),
+        (BoolAnd, _, Num(Bool(false))) => ret_kind(Num(Bool(false))),
+        (BoolAnd, _, _) if x == y => ret_ref(x),
+        (BoolOr, Num(Bool(true)), _) => ret_kind(Num(Bool(true))),
+        (BoolOr, _, Num(Bool(true))) => ret_kind(Num(Bool(true))),
+        (BoolOr, Num(Bool(false)), _) => ret_ref(y),
+        (BoolOr, _, Num(Bool(false))) => ret_ref(x),
+        (BoolOr, _, _) if x == y => ret_ref(x),
+        (BoolEQ, Num(Bool(true)), _) => ret_ref(y),
+        (BoolEQ, _, Num(Bool(true))) => ret_ref(x),
+        (BoolEQ, Num(Bool(x)), Num(Bool(y))) => ret_kind(Num(Bool(x == y))),
+        (BoolEQ, _, _) if x == y => ret_kind(Num(Bool(true))),
+        (BoolNE, Num(Bool(false)), _) => ret_ref(y),
+        (BoolNE, _, Num(Bool(false))) => ret_ref(x),
+        (BoolNE, Num(Bool(x)), Num(Bool(y))) => ret_kind(Num(Bool(x != y))),
+        (BoolNE, _, _) if x == y => ret_kind(Num(Bool(false))),
+
+        (NaturalPlus, Num(Natural(0)), _) => ret_ref(y),
+        (NaturalPlus, _, Num(Natural(0))) => ret_ref(x),
+        (NaturalPlus, Num(Natural(x)), Num(Natural(y))) => {
+            ret_kind(Num(Natural(x + y)))
+        }
+        (NaturalTimes, Num(Natural(0)), _) => ret_kind(Num(Natural(0))),
+        (NaturalTimes, _, Num(Natural(0))) => ret_kind(Num(Natural(0))),
+        (NaturalTimes, Num(Natural(1)), _) => ret_ref(y),
+        (NaturalTimes, _, Num(Natural(1))) => ret_ref(x),
+        (NaturalTimes, Num(Natural(x)), Num(Natural(y))) => {
+            ret_kind(Num(Natural(x * y)))
+        }
+
+        (ListAppend, EmptyListLit(_), _) => ret_ref(y),
+        (ListAppend, _, EmptyListLit(_)) => ret_ref(x),
+        (ListAppend, NEListLit(xs), NEListLit(ys)) => {
+            ret_kind(NEListLit(xs.iter().chain(ys.iter()).cloned().collect()))
+        }
+
+        (TextAppend, NirKind::TextLit(x), _) if x.is_empty() => ret_ref(y),
+        (TextAppend, _, NirKind::TextLit(y)) if y.is_empty() => ret_ref(x),
+        (TextAppend, NirKind::TextLit(x), NirKind::TextLit(y)) => {
+            ret_kind(NirKind::TextLit(x.concat(y)))
+        }
+        (TextAppend, NirKind::TextLit(x), _) => ret_kind(NirKind::TextLit(
+            x.concat(&TextLit::interpolate(y.clone())),
+        )),
+        (TextAppend, _, NirKind::TextLit(y)) => ret_kind(NirKind::TextLit(
+            TextLit::interpolate(x.clone()).concat(y),
+        )),
+
+        (RightBiasedRecordMerge, _, RecordLit(kvs)) if kvs.is_empty() => {
+            ret_ref(x)
+        }
+        (RightBiasedRecordMerge, RecordLit(kvs), _) if kvs.is_empty() => {
+            ret_ref(y)
+        }
+        (RightBiasedRecordMerge, RecordLit(kvs1), RecordLit(kvs2)) => {
+            let mut kvs = kvs2.clone();
+            for (x, v) in kvs1 {
+                // Insert only if key not already present
+                kvs.entry(x.clone()).or_insert_with(|| v.clone());
+            }
+            ret_kind(RecordLit(kvs))
+        }
+        (RightBiasedRecordMerge, _, _) if x == y => ret_ref(y),
+
+        (RecursiveRecordMerge, _, RecordLit(kvs)) if kvs.is_empty() => {
+            ret_ref(x)
+        }
+        (RecursiveRecordMerge, RecordLit(kvs), _) if kvs.is_empty() => {
+            ret_ref(y)
+        }
+        (RecursiveRecordMerge, RecordLit(kvs1), RecordLit(kvs2)) => {
+            let kvs = merge_maps(kvs1, kvs2, |_, v1, v2| {
+                Nir::from_partial_expr(ExprKind::Op(OpKind::BinOp(
+                    RecursiveRecordMerge,
+                    v1.clone(),
+                    v2.clone(),
+                )))
+            });
+            ret_kind(RecordLit(kvs))
+        }
+
+        (RecursiveRecordTypeMerge, RecordType(kts_x), RecordType(kts_y)) => {
+            let kts = merge_maps(
+                kts_x,
+                kts_y,
+                // If the Label exists for both records, then we hit the recursive case.
+                |_, l: &Nir, r: &Nir| {
+                    Nir::from_partial_expr(ExprKind::Op(OpKind::BinOp(
+                        RecursiveRecordTypeMerge,
+                        l.clone(),
+                        r.clone(),
+                    )))
+                },
+            );
+            ret_kind(RecordType(kts))
+        }
+
+        (Equivalence, _, _) => {
+            ret_kind(NirKind::Equivalence(x.clone(), y.clone()))
+        }
+
+        _ => ret_op(OpKind::BinOp(o, x.clone(), y.clone())),
+    }
+}
+
+fn normalize_field(v: &Nir, field: &Label) -> Ret {
+    use self::BinOp::{RecursiveRecordMerge, RightBiasedRecordMerge};
+    use NirKind::{Op, RecordLit, UnionConstructor, UnionType};
+    use OpKind::{BinOp, Field, Projection};
+    let nothing_to_do = || ret_op(Field(v.clone(), field.clone()));
+
+    match v.kind() {
+        RecordLit(kvs) => match kvs.get(field) {
+            Some(r) => ret_ref(r),
+            None => nothing_to_do(),
+        },
+        UnionType(kts) => {
+            ret_kind(UnionConstructor(field.clone(), kts.clone()))
+        }
+        Op(Projection(x, _)) => normalize_field(x, field),
+        Op(BinOp(RightBiasedRecordMerge, x, y)) => match (x.kind(), y.kind()) {
+            (_, RecordLit(kvs)) => match kvs.get(field) {
+                Some(r) => ret_ref(r),
+                None => normalize_field(x, field),
+            },
+            (RecordLit(kvs), _) => match kvs.get(field) {
+                Some(r) => ret_op(Field(
+                    Nir::from_kind(Op(BinOp(
+                        RightBiasedRecordMerge,
+                        Nir::from_kind(RecordLit(
+                            Some((field.clone(), r.clone()))
+                                .into_iter()
+                                .collect(),
+                        )),
+                        y.clone(),
+                    ))),
+                    field.clone(),
+                )),
+                None => normalize_field(y, field),
+            },
+            _ => nothing_to_do(),
+        },
+        Op(BinOp(RecursiveRecordMerge, x, y)) => match (x.kind(), y.kind()) {
+            (RecordLit(kvs), _) => match kvs.get(field) {
+                Some(r) => ret_op(Field(
+                    Nir::from_kind(Op(BinOp(
+                        RecursiveRecordMerge,
+                        Nir::from_kind(RecordLit(
+                            Some((field.clone(), r.clone()))
+                                .into_iter()
+                                .collect(),
+                        )),
+                        y.clone(),
+                    ))),
+                    field.clone(),
+                )),
+                None => normalize_field(y, field),
+            },
+            (_, RecordLit(kvs)) => match kvs.get(field) {
+                Some(r) => ret_op(Field(
+                    Nir::from_kind(Op(BinOp(
+                        RecursiveRecordMerge,
+                        x.clone(),
+                        Nir::from_kind(RecordLit(
+                            Some((field.clone(), r.clone()))
+                                .into_iter()
+                                .collect(),
+                        )),
+                    ))),
+                    field.clone(),
+                )),
+                None => normalize_field(x, field),
+            },
+            _ => nothing_to_do(),
+        },
+        _ => nothing_to_do(),
+    }
+}
+
+pub fn normalize_operation(opkind: &OpKind<Nir>) -> Ret {
+    use NirKind::{
+        EmptyListLit, EmptyOptionalLit, NEListLit, NEOptionalLit, Num, Op,
+        RecordLit, RecordType, UnionConstructor, UnionLit,
+    };
+    use NumKind::Bool;
+    use OpKind::*;
+    let nothing_to_do = || ret_op(opkind.clone());
+
+    match opkind {
+        App(v, a) => ret_kind(v.app_to_kind(a.clone())),
+        BinOp(o, x, y) => normalize_binop(*o, x, y),
+        BoolIf(b, e1, e2) => {
+            match b.kind() {
+                Num(Bool(true)) => ret_ref(e1),
+                Num(Bool(false)) => ret_ref(e2),
+                _ => {
+                    match (e1.kind(), e2.kind()) {
+                        // Simplify `if b then True else False`
+                        (Num(Bool(true)), Num(Bool(false))) => ret_ref(b),
+                        _ if e1 == e2 => ret_ref(e1),
+                        _ => nothing_to_do(),
+                    }
+                }
+            }
+        }
+        Merge(handlers, variant, _) => match handlers.kind() {
+            RecordLit(kvs) => match variant.kind() {
+                UnionConstructor(l, _) => match kvs.get(l) {
+                    Some(h) => ret_ref(h),
+                    None => nothing_to_do(),
+                },
+                UnionLit(l, v, _) => match kvs.get(l) {
+                    Some(h) => ret_kind(h.app_to_kind(v.clone())),
+                    None => nothing_to_do(),
+                },
+                EmptyOptionalLit(_) => match kvs.get(&"None".into()) {
+                    Some(h) => ret_ref(h),
+                    None => nothing_to_do(),
+                },
+                NEOptionalLit(v) => match kvs.get(&"Some".into()) {
+                    Some(h) => ret_kind(h.app_to_kind(v.clone())),
+                    None => nothing_to_do(),
+                },
+                _ => nothing_to_do(),
+            },
+            _ => nothing_to_do(),
+        },
+        ToMap(v, annot) => match v.kind() {
+            RecordLit(kvs) if kvs.is_empty() => {
+                match annot.as_ref().map(|v| v.kind()) {
+                    Some(NirKind::ListType(t)) => {
+                        ret_kind(EmptyListLit(t.clone()))
+                    }
+                    _ => nothing_to_do(),
+                }
+            }
+            RecordLit(kvs) => ret_kind(NEListLit(
+                kvs.iter()
+                    .sorted_by_key(|(k, _)| *k)
+                    .map(|(k, v)| {
+                        let mut rec = HashMap::new();
+                        rec.insert("mapKey".into(), Nir::from_text(k));
+                        rec.insert("mapValue".into(), v.clone());
+                        Nir::from_kind(NirKind::RecordLit(rec))
+                    })
+                    .collect(),
+            )),
+            _ => nothing_to_do(),
+        },
+        Field(v, field) => normalize_field(v, field),
+        Projection(_, ls) if ls.is_empty() => {
+            ret_kind(RecordLit(HashMap::new()))
+        }
+        Projection(v, ls) => match v.kind() {
+            RecordLit(kvs) => ret_kind(RecordLit(
+                ls.iter()
+                    .filter_map(|l| kvs.get(l).map(|x| (l.clone(), x.clone())))
+                    .collect(),
+            )),
+            Op(Projection(v2, _)) => {
+                normalize_operation(&Projection(v2.clone(), ls.clone()))
+            }
+            _ => nothing_to_do(),
+        },
+        ProjectionByExpr(v, t) => match t.kind() {
+            RecordType(kts) => normalize_operation(&Projection(
+                v.clone(),
+                kts.keys().cloned().collect(),
+            )),
+            _ => nothing_to_do(),
+        },
+        Completion(..) => {
+            unreachable!("This case should have been handled in resolution")
+        }
+    }
+}
diff --git a/dhall/src/semantics/builtins.rs b/dhall/src/semantics/builtins.rs
index 45be448..f65e8d1 100644
--- a/dhall/src/semantics/builtins.rs
+++ b/dhall/src/semantics/builtins.rs
@@ -1,3 +1,4 @@
+use crate::operations::OpKind;
 use crate::semantics::{
     skip_resolve_expr, typecheck, Hir, HirKind, Nir, NirKind, NzEnv, VarEnv,
 };
@@ -5,8 +6,8 @@ use crate::syntax::map::DupTreeMap;
 use crate::syntax::Const::Type;
 use crate::syntax::{
     BinOp, Builtin, Const, Expr, ExprKind, InterpolatedText,
-    InterpolatedTextContents, Label, NaiveDouble, NumKind, OpKind, Span,
-    UnspannedExpr, V,
+    InterpolatedTextContents, Label, NaiveDouble, NumKind, Span, UnspannedExpr,
+    V,
 };
 use std::collections::HashMap;
 use std::convert::TryInto;
diff --git a/dhall/src/semantics/nze/nir.rs b/dhall/src/semantics/nze/nir.rs
index 88123d8..5c67c02 100644
--- a/dhall/src/semantics/nze/nir.rs
+++ b/dhall/src/semantics/nze/nir.rs
@@ -1,6 +1,7 @@
 use std::collections::HashMap;
 use std::rc::Rc;
 
+use crate::operations::OpKind;
 use crate::semantics::nze::lazy;
 use crate::semantics::{
     apply_any, normalize_hir, normalize_one_layer, squash_textlit, Binder,
@@ -8,7 +9,7 @@ use crate::semantics::{
 };
 use crate::syntax::{
     BinOp, Builtin, Const, Expr, ExprKind, InterpolatedTextContents, Label,
-    NumKind, OpKind, Span,
+    NumKind, Span,
 };
 use crate::ToExprOptions;
 
diff --git a/dhall/src/semantics/nze/normalize.rs b/dhall/src/semantics/nze/normalize.rs
index c0e41cb..d042f3f 100644
--- a/dhall/src/semantics/nze/normalize.rs
+++ b/dhall/src/semantics/nze/normalize.rs
@@ -1,11 +1,9 @@
-use itertools::Itertools;
 use std::collections::HashMap;
 
+use crate::operations::{normalize_operation, OpKind};
 use crate::semantics::NzEnv;
 use crate::semantics::{Binder, Closure, Hir, HirKind, Nir, NirKind, TextLit};
-use crate::syntax::{
-    BinOp, ExprKind, InterpolatedTextContents, Label, NumKind, OpKind,
-};
+use crate::syntax::{ExprKind, InterpolatedTextContents};
 
 pub fn apply_any(f: &Nir, a: Nir) -> NirKind {
     match f.kind() {
@@ -83,306 +81,21 @@ where
     kvs
 }
 
-type Ret = NirKind;
+pub type Ret = NirKind;
 
-fn ret_nir(x: Nir) -> Ret {
+pub fn ret_nir(x: Nir) -> Ret {
     ret_ref(&x)
 }
-fn ret_kind(x: NirKind) -> Ret {
+pub fn ret_kind(x: NirKind) -> Ret {
     x
 }
-fn ret_ref(x: &Nir) -> Ret {
+pub fn ret_ref(x: &Nir) -> Ret {
     x.kind().clone()
 }
-fn ret_op(x: OpKind<Nir>) -> Ret {
+pub fn ret_op(x: OpKind<Nir>) -> Ret {
     NirKind::Op(x)
 }
 
-fn normalize_binop(o: BinOp, x: &Nir, y: &Nir) -> Ret {
-    use BinOp::*;
-    use NirKind::{EmptyListLit, NEListLit, Num, RecordLit, RecordType};
-    use NumKind::{Bool, Natural};
-
-    match (o, x.kind(), y.kind()) {
-        (BoolAnd, Num(Bool(true)), _) => ret_ref(y),
-        (BoolAnd, _, Num(Bool(true))) => ret_ref(x),
-        (BoolAnd, Num(Bool(false)), _) => ret_kind(Num(Bool(false))),
-        (BoolAnd, _, Num(Bool(false))) => ret_kind(Num(Bool(false))),
-        (BoolAnd, _, _) if x == y => ret_ref(x),
-        (BoolOr, Num(Bool(true)), _) => ret_kind(Num(Bool(true))),
-        (BoolOr, _, Num(Bool(true))) => ret_kind(Num(Bool(true))),
-        (BoolOr, Num(Bool(false)), _) => ret_ref(y),
-        (BoolOr, _, Num(Bool(false))) => ret_ref(x),
-        (BoolOr, _, _) if x == y => ret_ref(x),
-        (BoolEQ, Num(Bool(true)), _) => ret_ref(y),
-        (BoolEQ, _, Num(Bool(true))) => ret_ref(x),
-        (BoolEQ, Num(Bool(x)), Num(Bool(y))) => ret_kind(Num(Bool(x == y))),
-        (BoolEQ, _, _) if x == y => ret_kind(Num(Bool(true))),
-        (BoolNE, Num(Bool(false)), _) => ret_ref(y),
-        (BoolNE, _, Num(Bool(false))) => ret_ref(x),
-        (BoolNE, Num(Bool(x)), Num(Bool(y))) => ret_kind(Num(Bool(x != y))),
-        (BoolNE, _, _) if x == y => ret_kind(Num(Bool(false))),
-
-        (NaturalPlus, Num(Natural(0)), _) => ret_ref(y),
-        (NaturalPlus, _, Num(Natural(0))) => ret_ref(x),
-        (NaturalPlus, Num(Natural(x)), Num(Natural(y))) => {
-            ret_kind(Num(Natural(x + y)))
-        }
-        (NaturalTimes, Num(Natural(0)), _) => ret_kind(Num(Natural(0))),
-        (NaturalTimes, _, Num(Natural(0))) => ret_kind(Num(Natural(0))),
-        (NaturalTimes, Num(Natural(1)), _) => ret_ref(y),
-        (NaturalTimes, _, Num(Natural(1))) => ret_ref(x),
-        (NaturalTimes, Num(Natural(x)), Num(Natural(y))) => {
-            ret_kind(Num(Natural(x * y)))
-        }
-
-        (ListAppend, EmptyListLit(_), _) => ret_ref(y),
-        (ListAppend, _, EmptyListLit(_)) => ret_ref(x),
-        (ListAppend, NEListLit(xs), NEListLit(ys)) => {
-            ret_kind(NEListLit(xs.iter().chain(ys.iter()).cloned().collect()))
-        }
-
-        (TextAppend, NirKind::TextLit(x), _) if x.is_empty() => ret_ref(y),
-        (TextAppend, _, NirKind::TextLit(y)) if y.is_empty() => ret_ref(x),
-        (TextAppend, NirKind::TextLit(x), NirKind::TextLit(y)) => {
-            ret_kind(NirKind::TextLit(x.concat(y)))
-        }
-        (TextAppend, NirKind::TextLit(x), _) => ret_kind(NirKind::TextLit(
-            x.concat(&TextLit::interpolate(y.clone())),
-        )),
-        (TextAppend, _, NirKind::TextLit(y)) => ret_kind(NirKind::TextLit(
-            TextLit::interpolate(x.clone()).concat(y),
-        )),
-
-        (RightBiasedRecordMerge, _, RecordLit(kvs)) if kvs.is_empty() => {
-            ret_ref(x)
-        }
-        (RightBiasedRecordMerge, RecordLit(kvs), _) if kvs.is_empty() => {
-            ret_ref(y)
-        }
-        (RightBiasedRecordMerge, RecordLit(kvs1), RecordLit(kvs2)) => {
-            let mut kvs = kvs2.clone();
-            for (x, v) in kvs1 {
-                // Insert only if key not already present
-                kvs.entry(x.clone()).or_insert_with(|| v.clone());
-            }
-            ret_kind(RecordLit(kvs))
-        }
-        (RightBiasedRecordMerge, _, _) if x == y => ret_ref(y),
-
-        (RecursiveRecordMerge, _, RecordLit(kvs)) if kvs.is_empty() => {
-            ret_ref(x)
-        }
-        (RecursiveRecordMerge, RecordLit(kvs), _) if kvs.is_empty() => {
-            ret_ref(y)
-        }
-        (RecursiveRecordMerge, RecordLit(kvs1), RecordLit(kvs2)) => {
-            let kvs = merge_maps(kvs1, kvs2, |_, v1, v2| {
-                Nir::from_partial_expr(ExprKind::Op(OpKind::BinOp(
-                    RecursiveRecordMerge,
-                    v1.clone(),
-                    v2.clone(),
-                )))
-            });
-            ret_kind(RecordLit(kvs))
-        }
-
-        (RecursiveRecordTypeMerge, RecordType(kts_x), RecordType(kts_y)) => {
-            let kts = merge_maps(
-                kts_x,
-                kts_y,
-                // If the Label exists for both records, then we hit the recursive case.
-                |_, l: &Nir, r: &Nir| {
-                    Nir::from_partial_expr(ExprKind::Op(OpKind::BinOp(
-                        RecursiveRecordTypeMerge,
-                        l.clone(),
-                        r.clone(),
-                    )))
-                },
-            );
-            ret_kind(RecordType(kts))
-        }
-
-        (Equivalence, _, _) => {
-            ret_kind(NirKind::Equivalence(x.clone(), y.clone()))
-        }
-
-        _ => ret_op(OpKind::BinOp(o, x.clone(), y.clone())),
-    }
-}
-
-fn normalize_field(v: &Nir, field: &Label) -> Ret {
-    use self::BinOp::{RecursiveRecordMerge, RightBiasedRecordMerge};
-    use NirKind::{Op, RecordLit, UnionConstructor, UnionType};
-    use OpKind::{BinOp, Field, Projection};
-    let nothing_to_do = || ret_op(Field(v.clone(), field.clone()));
-
-    match v.kind() {
-        RecordLit(kvs) => match kvs.get(field) {
-            Some(r) => ret_ref(r),
-            None => nothing_to_do(),
-        },
-        UnionType(kts) => {
-            ret_kind(UnionConstructor(field.clone(), kts.clone()))
-        }
-        Op(Projection(x, _)) => normalize_field(x, field),
-        Op(BinOp(RightBiasedRecordMerge, x, y)) => match (x.kind(), y.kind()) {
-            (_, RecordLit(kvs)) => match kvs.get(field) {
-                Some(r) => ret_ref(r),
-                None => normalize_field(x, field),
-            },
-            (RecordLit(kvs), _) => match kvs.get(field) {
-                Some(r) => ret_op(Field(
-                    Nir::from_kind(Op(BinOp(
-                        RightBiasedRecordMerge,
-                        Nir::from_kind(RecordLit(
-                            Some((field.clone(), r.clone()))
-                                .into_iter()
-                                .collect(),
-                        )),
-                        y.clone(),
-                    ))),
-                    field.clone(),
-                )),
-                None => normalize_field(y, field),
-            },
-            _ => nothing_to_do(),
-        },
-        Op(BinOp(RecursiveRecordMerge, x, y)) => match (x.kind(), y.kind()) {
-            (RecordLit(kvs), _) => match kvs.get(field) {
-                Some(r) => ret_op(Field(
-                    Nir::from_kind(Op(BinOp(
-                        RecursiveRecordMerge,
-                        Nir::from_kind(RecordLit(
-                            Some((field.clone(), r.clone()))
-                                .into_iter()
-                                .collect(),
-                        )),
-                        y.clone(),
-                    ))),
-                    field.clone(),
-                )),
-                None => normalize_field(y, field),
-            },
-            (_, RecordLit(kvs)) => match kvs.get(field) {
-                Some(r) => ret_op(Field(
-                    Nir::from_kind(Op(BinOp(
-                        RecursiveRecordMerge,
-                        x.clone(),
-                        Nir::from_kind(RecordLit(
-                            Some((field.clone(), r.clone()))
-                                .into_iter()
-                                .collect(),
-                        )),
-                    ))),
-                    field.clone(),
-                )),
-                None => normalize_field(x, field),
-            },
-            _ => nothing_to_do(),
-        },
-        _ => nothing_to_do(),
-    }
-}
-
-fn normalize_operation(opkind: &OpKind<Nir>) -> Ret {
-    use NirKind::{
-        EmptyListLit, EmptyOptionalLit, NEListLit, NEOptionalLit, Num, Op,
-        RecordLit, RecordType, UnionConstructor, UnionLit,
-    };
-    use NumKind::Bool;
-    use OpKind::*;
-    let nothing_to_do = || ret_op(opkind.clone());
-
-    match opkind {
-        App(v, a) => ret_kind(v.app_to_kind(a.clone())),
-        BinOp(o, x, y) => normalize_binop(*o, x, y),
-        BoolIf(b, e1, e2) => {
-            match b.kind() {
-                Num(Bool(true)) => ret_ref(e1),
-                Num(Bool(false)) => ret_ref(e2),
-                _ => {
-                    match (e1.kind(), e2.kind()) {
-                        // Simplify `if b then True else False`
-                        (Num(Bool(true)), Num(Bool(false))) => ret_ref(b),
-                        _ if e1 == e2 => ret_ref(e1),
-                        _ => nothing_to_do(),
-                    }
-                }
-            }
-        }
-        Merge(handlers, variant, _) => match handlers.kind() {
-            RecordLit(kvs) => match variant.kind() {
-                UnionConstructor(l, _) => match kvs.get(l) {
-                    Some(h) => ret_ref(h),
-                    None => nothing_to_do(),
-                },
-                UnionLit(l, v, _) => match kvs.get(l) {
-                    Some(h) => ret_kind(h.app_to_kind(v.clone())),
-                    None => nothing_to_do(),
-                },
-                EmptyOptionalLit(_) => match kvs.get(&"None".into()) {
-                    Some(h) => ret_ref(h),
-                    None => nothing_to_do(),
-                },
-                NEOptionalLit(v) => match kvs.get(&"Some".into()) {
-                    Some(h) => ret_kind(h.app_to_kind(v.clone())),
-                    None => nothing_to_do(),
-                },
-                _ => nothing_to_do(),
-            },
-            _ => nothing_to_do(),
-        },
-        ToMap(v, annot) => match v.kind() {
-            RecordLit(kvs) if kvs.is_empty() => {
-                match annot.as_ref().map(|v| v.kind()) {
-                    Some(NirKind::ListType(t)) => {
-                        ret_kind(EmptyListLit(t.clone()))
-                    }
-                    _ => nothing_to_do(),
-                }
-            }
-            RecordLit(kvs) => ret_kind(NEListLit(
-                kvs.iter()
-                    .sorted_by_key(|(k, _)| *k)
-                    .map(|(k, v)| {
-                        let mut rec = HashMap::new();
-                        rec.insert("mapKey".into(), Nir::from_text(k));
-                        rec.insert("mapValue".into(), v.clone());
-                        Nir::from_kind(NirKind::RecordLit(rec))
-                    })
-                    .collect(),
-            )),
-            _ => nothing_to_do(),
-        },
-        Field(v, field) => normalize_field(v, field),
-        Projection(_, ls) if ls.is_empty() => {
-            ret_kind(RecordLit(HashMap::new()))
-        }
-        Projection(v, ls) => match v.kind() {
-            RecordLit(kvs) => ret_kind(RecordLit(
-                ls.iter()
-                    .filter_map(|l| kvs.get(l).map(|x| (l.clone(), x.clone())))
-                    .collect(),
-            )),
-            Op(Projection(v2, _)) => {
-                normalize_operation(&Projection(v2.clone(), ls.clone()))
-            }
-            _ => nothing_to_do(),
-        },
-        ProjectionByExpr(v, t) => match t.kind() {
-            RecordType(kts) => normalize_operation(&Projection(
-                v.clone(),
-                kts.keys().cloned().collect(),
-            )),
-            _ => nothing_to_do(),
-        },
-        Completion(..) => {
-            unreachable!("This case should have been handled in resolution")
-        }
-    }
-}
-
 pub fn normalize_one_layer(expr: ExprKind<Nir>, env: &NzEnv) -> NirKind {
     use NirKind::{
         Assert, Const, NEListLit, NEOptionalLit, Num, RecordLit, RecordType,
diff --git a/dhall/src/semantics/resolve/resolve.rs b/dhall/src/semantics/resolve/resolve.rs
index 3e0022f..bbcd240 100644
--- a/dhall/src/semantics/resolve/resolve.rs
+++ b/dhall/src/semantics/resolve/resolve.rs
@@ -6,12 +6,13 @@ use url::Url;
 
 use crate::error::ErrorBuilder;
 use crate::error::{Error, ImportError};
+use crate::operations::OpKind;
 use crate::semantics::{mkerr, Hir, HirKind, ImportEnv, NameEnv, Type};
 use crate::syntax;
 use crate::syntax::map::DupTreeMap;
 use crate::syntax::{
     BinOp, Builtin, Expr, ExprKind, FilePath, FilePrefix, Hash, ImportMode,
-    ImportTarget, OpKind, Span, UnspannedExpr, URL,
+    ImportTarget, Span, UnspannedExpr, URL,
 };
 use crate::{Parsed, Resolved};
 
diff --git a/dhall/src/semantics/tck/typecheck.rs b/dhall/src/semantics/tck/typecheck.rs
index 427b39d..7481f07 100644
--- a/dhall/src/semantics/tck/typecheck.rs
+++ b/dhall/src/semantics/tck/typecheck.rs
@@ -1,51 +1,15 @@
-use std::borrow::Cow;
 use std::cmp::max;
 use std::collections::HashMap;
 
 use crate::error::{ErrorBuilder, TypeError, TypeMessage};
-use crate::semantics::merge_maps;
+use crate::operations::typecheck_operation;
 use crate::semantics::{
-    type_of_builtin, Binder, Closure, Hir, HirKind, Nir, NirKind, Tir, TyEnv,
-    Type,
+    type_of_builtin, Hir, HirKind, Nir, NirKind, Tir, TyEnv, Type,
 };
 use crate::syntax::{
-    BinOp, Builtin, Const, ExprKind, InterpolatedTextContents, NumKind, OpKind,
-    Span,
+    Builtin, Const, ExprKind, InterpolatedTextContents, NumKind, Span,
 };
 
-fn check_rectymerge(
-    span: &Span,
-    env: &TyEnv,
-    x: Nir,
-    y: Nir,
-) -> Result<(), TypeError> {
-    let kts_x = match x.kind() {
-        NirKind::RecordType(kts) => kts,
-        _ => {
-            return mk_span_err(
-                span.clone(),
-                "RecordTypeMergeRequiresRecordType",
-            )
-        }
-    };
-    let kts_y = match y.kind() {
-        NirKind::RecordType(kts) => kts,
-        _ => {
-            return mk_span_err(
-                span.clone(),
-                "RecordTypeMergeRequiresRecordType",
-            )
-        }
-    };
-    for (k, tx) in kts_x {
-        if let Some(ty) = kts_y.get(k) {
-            // TODO: store Type in RecordType ?
-            check_rectymerge(span, env, tx.clone(), ty.clone())?;
-        }
-    }
-    Ok(())
-}
-
 fn function_check(a: Const, b: Const) -> Const {
     if b == Const::Type {
         Const::Type
@@ -66,477 +30,6 @@ pub fn mk_span_err<T, S: ToString>(span: Span, msg: S) -> Result<T, TypeError> {
     )
 }
 
-fn type_of_binop(
-    env: &TyEnv,
-    span: Span,
-    op: BinOp,
-    l: &Tir<'_>,
-    r: &Tir<'_>,
-) -> Result<Type, TypeError> {
-    let span_err = |msg: &str| mk_span_err(span.clone(), msg);
-    use BinOp::*;
-    use NirKind::{ListType, RecordType};
-
-    Ok(match op {
-        RightBiasedRecordMerge => {
-            let x_type = l.ty();
-            let y_type = r.ty();
-
-            // Extract the LHS record type
-            let kts_x = match x_type.kind() {
-                RecordType(kts) => kts,
-                _ => return span_err("MustCombineRecord"),
-            };
-            // Extract the RHS record type
-            let kts_y = match y_type.kind() {
-                RecordType(kts) => kts,
-                _ => return span_err("MustCombineRecord"),
-            };
-
-            // Union the two records, prefering
-            // the values found in the RHS.
-            let kts = merge_maps(kts_x, kts_y, |_, _, r_t| r_t.clone());
-
-            let u = max(l.ty().ty(), r.ty().ty());
-            Nir::from_kind(RecordType(kts)).to_type(u)
-        }
-        RecursiveRecordMerge => {
-            check_rectymerge(&span, env, l.ty().to_nir(), r.ty().to_nir())?;
-
-            let hir = Hir::new(
-                HirKind::Expr(ExprKind::Op(OpKind::BinOp(
-                    RecursiveRecordTypeMerge,
-                    l.ty().to_hir(env.as_varenv()),
-                    r.ty().to_hir(env.as_varenv()),
-                ))),
-                span.clone(),
-            );
-            let x_u = l.ty().ty();
-            let y_u = r.ty().ty();
-            Type::new(hir.eval(env), max(x_u, y_u))
-        }
-        RecursiveRecordTypeMerge => {
-            check_rectymerge(&span, env, l.eval(env), r.eval(env))?;
-
-            // A RecordType's type is always a const
-            let xk = l.ty().as_const().unwrap();
-            let yk = r.ty().as_const().unwrap();
-            Type::from_const(max(xk, yk))
-        }
-        ListAppend => {
-            match l.ty().kind() {
-                ListType(..) => {}
-                _ => return span_err("BinOpTypeMismatch"),
-            }
-
-            if l.ty() != r.ty() {
-                return span_err("BinOpTypeMismatch");
-            }
-
-            l.ty().clone()
-        }
-        Equivalence => {
-            if l.ty() != r.ty() {
-                return span_err("EquivalenceTypeMismatch");
-            }
-            if l.ty().ty().as_const() != Some(Const::Type) {
-                return span_err("EquivalenceArgumentsMustBeTerms");
-            }
-
-            Type::from_const(Const::Type)
-        }
-        op => {
-            let t = Type::from_builtin(match op {
-                BoolAnd | BoolOr | BoolEQ | BoolNE => Builtin::Bool,
-                NaturalPlus | NaturalTimes => Builtin::Natural,
-                TextAppend => Builtin::Text,
-                ListAppend
-                | RightBiasedRecordMerge
-                | RecursiveRecordMerge
-                | RecursiveRecordTypeMerge
-                | Equivalence => unreachable!(),
-                ImportAlt => unreachable!("ImportAlt leftover in tck"),
-            });
-
-            if *l.ty() != t {
-                return span_err("BinOpTypeMismatch");
-            }
-
-            if *r.ty() != t {
-                return span_err("BinOpTypeMismatch");
-            }
-
-            t
-        }
-    })
-}
-
-fn type_of_merge(
-    env: &TyEnv,
-    span: Span,
-    record: &Tir<'_>,
-    scrut: &Tir<'_>,
-    type_annot: Option<&Tir<'_>>,
-) -> Result<Type, TypeError> {
-    let span_err = |msg: &str| mk_span_err(span.clone(), msg);
-    use NirKind::{OptionalType, PiClosure, RecordType, UnionType};
-
-    let record_type = record.ty();
-    let handlers = match record_type.kind() {
-        RecordType(kts) => kts,
-        _ => return span_err("Merge1ArgMustBeRecord"),
-    };
-
-    let scrut_type = scrut.ty();
-    let variants = match scrut_type.kind() {
-        UnionType(kts) => Cow::Borrowed(kts),
-        OptionalType(ty) => {
-            let mut kts = HashMap::new();
-            kts.insert("None".into(), None);
-            kts.insert("Some".into(), Some(ty.clone()));
-            Cow::Owned(kts)
-        }
-        _ => return span_err("Merge2ArgMustBeUnionOrOptional"),
-    };
-
-    let mut inferred_type = None;
-    for (x, handler_type) in handlers {
-        let handler_return_type: Type = match variants.get(x) {
-            // Union alternative with type
-            Some(Some(variant_type)) => match handler_type.kind() {
-                PiClosure { closure, annot, .. } => {
-                    if variant_type != annot {
-                        return mkerr(
-                            ErrorBuilder::new(format!(
-                                "Wrong handler input type"
-                            ))
-                            .span_err(
-                                span,
-                                format!("in this merge expression",),
-                            )
-                            .span_err(
-                                record.span(),
-                                format!(
-                                    "the handler for `{}` expects a value of \
-                                     type: `{}`",
-                                    x,
-                                    annot.to_expr_tyenv(env)
-                                ),
-                            )
-                            .span_err(
-                                scrut.span(),
-                                format!(
-                                    "but the corresponding variant has type: \
-                                     `{}`",
-                                    variant_type.to_expr_tyenv(env)
-                                ),
-                            )
-                            .format(),
-                        );
-                    }
-
-                    // TODO: this actually doesn't check anything yet
-                    match closure.remove_binder() {
-                        Ok(v) => Type::new_infer_universe(env, v.clone())?,
-                        Err(()) => {
-                            return span_err("MergeReturnTypeIsDependent")
-                        }
-                    }
-                }
-                _ => {
-                    return mkerr(
-                        ErrorBuilder::new(format!(
-                            "merge handler is not a function"
-                        ))
-                        .span_err(span, format!("in this merge expression"))
-                        .span_err(
-                            record.span(),
-                            format!(
-                                "the handler for `{}` has type: `{}`",
-                                x,
-                                handler_type.to_expr_tyenv(env)
-                            ),
-                        )
-                        .span_help(
-                            scrut.span(),
-                            format!(
-                                "the corresponding variant has type: `{}`",
-                                variant_type.to_expr_tyenv(env)
-                            ),
-                        )
-                        .help(format!(
-                            "a handler for this variant must be a function \
-                             that takes an input of type: `{}`",
-                            variant_type.to_expr_tyenv(env)
-                        ))
-                        .format(),
-                    )
-                }
-            },
-            // Union alternative without type
-            Some(None) => Type::new_infer_universe(env, handler_type.clone())?,
-            None => return span_err("MergeHandlerMissingVariant"),
-        };
-        match &inferred_type {
-            None => inferred_type = Some(handler_return_type),
-            Some(t) => {
-                if t != &handler_return_type {
-                    return span_err("MergeHandlerTypeMismatch");
-                }
-            }
-        }
-    }
-    for x in variants.keys() {
-        if !handlers.contains_key(x) {
-            return span_err("MergeVariantMissingHandler");
-        }
-    }
-
-    let type_annot = type_annot
-        .as_ref()
-        .map(|t| t.eval_to_type(env))
-        .transpose()?;
-    Ok(match (inferred_type, type_annot) {
-        (Some(t1), Some(t2)) => {
-            if t1 != t2 {
-                return span_err("MergeAnnotMismatch");
-            }
-            t1
-        }
-        (Some(t), None) => t,
-        (None, Some(t)) => t,
-        (None, None) => return span_err("MergeEmptyNeedsAnnotation"),
-    })
-}
-
-fn type_of_operation(
-    env: &TyEnv,
-    span: Span,
-    opkind: &OpKind<Tir<'_>>,
-) -> Result<Type, TypeError> {
-    let span_err = |msg: &str| mk_span_err(span.clone(), msg);
-    use NirKind::{ListType, PiClosure, RecordType, UnionType};
-    use OpKind::*;
-
-    Ok(match opkind {
-        App(f, arg) => {
-            match f.ty().kind() {
-                // TODO: store Type in closure
-                PiClosure { annot, closure, .. } => {
-                    if arg.ty().as_nir() != annot {
-                        return mkerr(
-                            ErrorBuilder::new(format!(
-                                "wrong type of function argument"
-                            ))
-                            .span_err(
-                                f.span(),
-                                format!(
-                                    "this expects an argument of type: {}",
-                                    annot.to_expr_tyenv(env),
-                                ),
-                            )
-                            .span_err(
-                                arg.span(),
-                                format!(
-                                    "but this has type: {}",
-                                    arg.ty().to_expr_tyenv(env),
-                                ),
-                            )
-                            .note(format!(
-                                "expected type `{}`\n   found type `{}`",
-                                annot.to_expr_tyenv(env),
-                                arg.ty().to_expr_tyenv(env),
-                            ))
-                            .format(),
-                        );
-                    }
-
-                    let arg_nf = arg.eval(env);
-                    Type::new_infer_universe(env, closure.apply(arg_nf))?
-                }
-                _ => return mkerr(
-                    ErrorBuilder::new(format!(
-                        "expected function, found `{}`",
-                        f.ty().to_expr_tyenv(env)
-                    ))
-                    .span_err(
-                        f.span(),
-                        format!("function application requires a function",),
-                    )
-                    .format(),
-                ),
-            }
-        }
-        BinOp(o, l, r) => type_of_binop(env, span, *o, l, r)?,
-        BoolIf(x, y, z) => {
-            if *x.ty().kind() != NirKind::from_builtin(Builtin::Bool) {
-                return span_err("InvalidPredicate");
-            }
-            if y.ty().ty().as_const() != Some(Const::Type) {
-                return span_err("IfBranchMustBeTerm");
-            }
-            if y.ty() != z.ty() {
-                return span_err("IfBranchMismatch");
-            }
-
-            y.ty().clone()
-        }
-        Merge(record, scrut, type_annot) => {
-            type_of_merge(env, span, record, scrut, type_annot.as_ref())?
-        }
-        ToMap(record, annot) => {
-            if record.ty().ty().as_const() != Some(Const::Type) {
-                return span_err("`toMap` only accepts records of type `Type`");
-            }
-            let record_t = record.ty();
-            let kts = match record_t.kind() {
-                RecordType(kts) => kts,
-                _ => {
-                    return span_err("The argument to `toMap` must be a record")
-                }
-            };
-
-            if kts.is_empty() {
-                let annot = if let Some(annot) = annot {
-                    annot
-                } else {
-                    return span_err(
-                        "`toMap` applied to an empty record requires a type \
-                         annotation",
-                    );
-                };
-                let annot_val = annot.eval_to_type(env)?;
-
-                let err_msg = "The type of `toMap x` must be of the form \
-                               `List { mapKey : Text, mapValue : T }`";
-                let arg = match annot_val.kind() {
-                    ListType(t) => t,
-                    _ => return span_err(err_msg),
-                };
-                let kts = match arg.kind() {
-                    RecordType(kts) => kts,
-                    _ => return span_err(err_msg),
-                };
-                if kts.len() != 2 {
-                    return span_err(err_msg);
-                }
-                match kts.get(&"mapKey".into()) {
-                    Some(t) if *t == Nir::from_builtin(Builtin::Text) => {}
-                    _ => return span_err(err_msg),
-                }
-                match kts.get(&"mapValue".into()) {
-                    Some(_) => {}
-                    None => return span_err(err_msg),
-                }
-                annot_val
-            } else {
-                let entry_type = kts.iter().next().unwrap().1.clone();
-                for (_, t) in kts.iter() {
-                    if *t != entry_type {
-                        return span_err(
-                            "Every field of the record must have the same type",
-                        );
-                    }
-                }
-
-                let mut kts = HashMap::new();
-                kts.insert("mapKey".into(), Nir::from_builtin(Builtin::Text));
-                kts.insert("mapValue".into(), entry_type);
-                let output_type: Type = Nir::from_builtin(Builtin::List)
-                    .app(Nir::from_kind(RecordType(kts)))
-                    .to_type(Const::Type);
-                if let Some(annot) = annot {
-                    let annot_val = annot.eval_to_type(env)?;
-                    if output_type != annot_val {
-                        return span_err("Annotation mismatch");
-                    }
-                }
-                output_type
-            }
-        }
-        Field(scrut, x) => {
-            match scrut.ty().kind() {
-                RecordType(kts) => match kts.get(&x) {
-                    Some(val) => Type::new_infer_universe(env, val.clone())?,
-                    None => return span_err("MissingRecordField"),
-                },
-                NirKind::Const(_) => {
-                    let scrut = scrut.eval_to_type(env)?;
-                    match scrut.kind() {
-                        UnionType(kts) => match kts.get(x) {
-                            // Constructor has type T -> < x: T, ... >
-                            Some(Some(ty)) => Nir::from_kind(PiClosure {
-                                binder: Binder::new(x.clone()),
-                                annot: ty.clone(),
-                                closure: Closure::new_constant(scrut.to_nir()),
-                            })
-                            .to_type(scrut.ty()),
-                            Some(None) => scrut,
-                            None => return span_err("MissingUnionField"),
-                        },
-                        _ => return span_err("NotARecord"),
-                    }
-                }
-                _ => return span_err("NotARecord"),
-            }
-        }
-        Projection(record, labels) => {
-            let record_type = record.ty();
-            let kts = match record_type.kind() {
-                RecordType(kts) => kts,
-                _ => return span_err("ProjectionMustBeRecord"),
-            };
-
-            let mut new_kts = HashMap::new();
-            for l in labels {
-                match kts.get(l) {
-                    None => return span_err("ProjectionMissingEntry"),
-                    Some(t) => {
-                        use std::collections::hash_map::Entry;
-                        match new_kts.entry(l.clone()) {
-                            Entry::Occupied(_) => {
-                                return span_err("ProjectionDuplicateField")
-                            }
-                            Entry::Vacant(e) => e.insert(t.clone()),
-                        }
-                    }
-                };
-            }
-
-            Type::new_infer_universe(env, Nir::from_kind(RecordType(new_kts)))?
-        }
-        ProjectionByExpr(record, selection) => {
-            let record_type = record.ty();
-            let rec_kts = match record_type.kind() {
-                RecordType(kts) => kts,
-                _ => return span_err("ProjectionMustBeRecord"),
-            };
-
-            let selection_val = selection.eval_to_type(env)?;
-            let sel_kts = match selection_val.kind() {
-                RecordType(kts) => kts,
-                _ => return span_err("ProjectionByExprTakesRecordType"),
-            };
-
-            for (l, sel_ty) in sel_kts {
-                match rec_kts.get(l) {
-                    Some(rec_ty) => {
-                        if rec_ty != sel_ty {
-                            return span_err("ProjectionWrongType");
-                        }
-                    }
-                    None => return span_err("ProjectionMissingEntry"),
-                }
-            }
-
-            selection_val
-        }
-        Completion(..) => {
-            unreachable!("This case should have been handled in resolution")
-        }
-    })
-}
-
 /// When all sub-expressions have been typed, check the remaining toplevel
 /// layer.
 fn type_one_layer(
@@ -690,7 +183,7 @@ fn type_one_layer(
 
             Type::from_const(k)
         }
-        ExprKind::Op(op) => type_of_operation(env, span, op)?,
+        ExprKind::Op(op) => typecheck_operation(env, span, op)?,
         ExprKind::Assert(t) => {
             let t = t.eval_to_type(env)?;
             match t.kind() {
diff --git a/dhall/src/syntax/ast/expr.rs b/dhall/src/syntax/ast/expr.rs
index 51e9ea7..62734bf 100644
--- a/dhall/src/syntax/ast/expr.rs
+++ b/dhall/src/syntax/ast/expr.rs
@@ -1,8 +1,9 @@
 use std::collections::BTreeMap;
 
 use crate::error::Error;
+use crate::operations::OpKind;
 use crate::semantics::Universe;
-use crate::syntax::map::{DupTreeMap, DupTreeSet};
+use crate::syntax::map::DupTreeMap;
 use crate::syntax::visitor;
 use crate::syntax::*;
 
@@ -126,29 +127,6 @@ pub enum NumKind {
     Double(Double),
 }
 
-/// Operations
-#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub enum OpKind<SubExpr> {
-    ///  `f a`
-    App(SubExpr, SubExpr),
-    /// Binary operations
-    BinOp(BinOp, SubExpr, SubExpr),
-    ///  `if x then y else z`
-    BoolIf(SubExpr, SubExpr, SubExpr),
-    ///  `merge x y : t`
-    Merge(SubExpr, SubExpr, Option<SubExpr>),
-    ///  `toMap x : t`
-    ToMap(SubExpr, Option<SubExpr>),
-    ///  `e.x`
-    Field(SubExpr, Label),
-    ///  `e.{ x, y, z }`
-    Projection(SubExpr, DupTreeSet<Label>),
-    ///  `e.(t)`
-    ProjectionByExpr(SubExpr, SubExpr),
-    ///  `x::y`
-    Completion(SubExpr, SubExpr),
-}
-
 /// Syntax tree for expressions
 // Having the recursion out of the enum definition enables writing
 // much more generic code and improves pattern-matching behind
@@ -249,45 +227,6 @@ impl<SE> ExprKind<SE> {
     }
 }
 
-impl<SE> OpKind<SE> {
-    pub fn traverse_ref<'a, SE2, Err>(
-        &'a self,
-        mut f: impl FnMut(&'a SE) -> Result<SE2, Err>,
-    ) -> Result<OpKind<SE2>, Err> {
-        // Can't use closures because of borrowing rules
-        macro_rules! expr {
-            ($e:expr) => {
-                f($e)?
-            };
-        }
-        macro_rules! opt {
-            ($e:expr) => {
-                $e.as_ref().map(|e| Ok(expr!(e))).transpose()?
-            };
-        }
-
-        use OpKind::*;
-        Ok(match self {
-            App(f, a) => App(expr!(f), expr!(a)),
-            BinOp(o, x, y) => BinOp(*o, expr!(x), expr!(y)),
-            BoolIf(b, t, f) => BoolIf(expr!(b), expr!(t), expr!(f)),
-            Merge(x, y, t) => Merge(expr!(x), expr!(y), opt!(t)),
-            ToMap(x, t) => ToMap(expr!(x), opt!(t)),
-            Field(e, l) => Field(expr!(e), l.clone()),
-            Projection(e, ls) => Projection(expr!(e), ls.clone()),
-            ProjectionByExpr(e, x) => ProjectionByExpr(expr!(e), expr!(x)),
-            Completion(e, x) => Completion(expr!(e), expr!(x)),
-        })
-    }
-
-    pub fn map_ref<'a, SE2>(
-        &'a self,
-        mut f: impl FnMut(&'a SE) -> SE2,
-    ) -> OpKind<SE2> {
-        trivial_result(self.traverse_ref(|x| Ok(f(x))))
-    }
-}
-
 impl Expr {
     pub fn as_ref(&self) -> &UnspannedExpr {
         &self.kind
diff --git a/dhall/src/syntax/binary/decode.rs b/dhall/src/syntax/binary/decode.rs
index b183f6c..f062089 100644
--- a/dhall/src/syntax/binary/decode.rs
+++ b/dhall/src/syntax/binary/decode.rs
@@ -3,10 +3,11 @@ use serde_cbor::value::value as cbor;
 use std::iter::FromIterator;
 
 use crate::error::DecodeError;
+use crate::operations::OpKind;
 use crate::syntax;
 use crate::syntax::{
     Expr, ExprKind, FilePath, FilePrefix, Hash, ImportMode, ImportTarget,
-    Integer, InterpolatedText, Label, Natural, NumKind, OpKind, Scheme, Span,
+    Integer, InterpolatedText, Label, Natural, NumKind, Scheme, Span,
     UnspannedExpr, URL, V,
 };
 type DecodedExpr = Expr;
diff --git a/dhall/src/syntax/binary/encode.rs b/dhall/src/syntax/binary/encode.rs
index f2bc6f1..cef2af8 100644
--- a/dhall/src/syntax/binary/encode.rs
+++ b/dhall/src/syntax/binary/encode.rs
@@ -3,11 +3,12 @@ use std::collections::BTreeMap;
 use std::vec;
 
 use crate::error::EncodeError;
+use crate::operations::OpKind;
 use crate::syntax;
 use crate::syntax::map::DupTreeMap;
 use crate::syntax::{
     Expr, ExprKind, FilePrefix, Hash, Import, ImportMode, ImportTarget, Label,
-    OpKind, Scheme, V,
+    Scheme, V,
 };
 
 pub fn encode(expr: &Expr) -> Result<Vec<u8>, EncodeError> {
@@ -49,7 +50,7 @@ where
     use syntax::Builtin;
     use syntax::ExprKind::*;
     use syntax::NumKind::*;
-    use syntax::OpKind::*;
+    use OpKind::*;
 
     use self::Serialize::{RecordDupMap, RecordMap, UnionMap};
     fn expr(x: &Expr) -> self::Serialize<'_> {
diff --git a/dhall/src/syntax/text/parser.rs b/dhall/src/syntax/text/parser.rs
index ab9bc24..8d76225 100644
--- a/dhall/src/syntax/text/parser.rs
+++ b/dhall/src/syntax/text/parser.rs
@@ -7,10 +7,10 @@ use std::rc::Rc;
 
 use pest_consume::{match_nodes, Parser};
 
+use crate::operations::OpKind::*;
 use crate::syntax::map::{DupTreeMap, DupTreeSet};
 use crate::syntax::ExprKind::*;
 use crate::syntax::NumKind::*;
-use crate::syntax::OpKind::*;
 use crate::syntax::{
     Double, Expr, FilePath, FilePrefix, Hash, ImportMode, ImportTarget,
     Integer, InterpolatedText, InterpolatedTextContents, Label, NaiveDouble,
diff --git a/dhall/src/syntax/text/printer.rs b/dhall/src/syntax/text/printer.rs
index d655489..a85f435 100644
--- a/dhall/src/syntax/text/printer.rs
+++ b/dhall/src/syntax/text/printer.rs
@@ -1,3 +1,4 @@
+use crate::operations::OpKind;
 use crate::syntax::*;
 use itertools::Itertools;
 use std::fmt::{self, Display};
@@ -37,8 +38,8 @@ impl<'a> PhasedExpr<'a> {
 impl UnspannedExpr {
     // Annotate subexpressions with the appropriate phase, defaulting to Base
     fn annotate_with_phases(&self) -> ExprKind<PhasedExpr<'_>> {
-        use crate::syntax::ExprKind::*;
-        use crate::syntax::OpKind::*;
+        use ExprKind::*;
+        use OpKind::*;
         use PrintPhase::*;
         let with_base = self.map_ref(|e| PhasedExpr(e, Base));
         match with_base {
@@ -89,8 +90,8 @@ impl UnspannedExpr {
         f: &mut fmt::Formatter,
         phase: PrintPhase,
     ) -> Result<(), fmt::Error> {
-        use crate::syntax::ExprKind::*;
-        use crate::syntax::OpKind::*;
+        use ExprKind::*;
+        use OpKind::*;
 
         let needs_paren = match self {
             Lam(_, _, _)
@@ -212,7 +213,7 @@ impl<SE: Display + Clone> Display for ExprKind<SE> {
 /// Generic instance that delegates to subexpressions
 impl<SE: Display + Clone> Display for OpKind<SE> {
     fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
-        use crate::syntax::OpKind::*;
+        use OpKind::*;
         match self {
             App(a, b) => {
                 write!(f, "{} {}", a, b)?;
diff --git a/serde_dhall/src/value.rs b/serde_dhall/src/value.rs
index 587349c..e8f333e 100644
--- a/serde_dhall/src/value.rs
+++ b/serde_dhall/src/value.rs
@@ -1,7 +1,8 @@
 use std::collections::{BTreeMap, HashMap};
 
+use dhall::operations::OpKind;
 use dhall::semantics::{Hir, HirKind, Nir, NirKind};
-use dhall::syntax::{Builtin, Expr, ExprKind, NumKind, OpKind, Span};
+use dhall::syntax::{Builtin, Expr, ExprKind, NumKind, Span};
 
 use crate::{Error, ErrorKind, FromDhall, Result, Sealed};
 
-- 
cgit v1.3.1


From 56efd2ac39149d8652bd625fbf0679c10823b137 Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Mon, 6 Apr 2020 22:24:15 +0100
Subject: Move BinOp and Builtin definitions in the relevant module

---
 dhall/src/builtins.rs                  | 122 +++++++++++++++++++++++++++++++--
 dhall/src/operations.rs                |  37 +++++++++-
 dhall/src/semantics/nze/nir.rs         |   7 +-
 dhall/src/semantics/resolve/resolve.rs |   7 +-
 dhall/src/semantics/tck/tir.rs         |   3 +-
 dhall/src/semantics/tck/typecheck.rs   |   6 +-
 dhall/src/syntax/ast/expr.rs           |  69 +------------------
 dhall/src/syntax/binary/decode.rs      |   4 +-
 dhall/src/syntax/binary/encode.rs      |   8 +--
 dhall/src/syntax/text/parser.rs        |  48 ++-----------
 dhall/src/syntax/text/printer.rs       |  48 ++-----------
 serde_dhall/src/value.rs               |   3 +-
 12 files changed, 182 insertions(+), 180 deletions(-)

(limited to 'dhall/src/semantics/resolve')

diff --git a/dhall/src/builtins.rs b/dhall/src/builtins.rs
index f65e8d1..bb8173c 100644
--- a/dhall/src/builtins.rs
+++ b/dhall/src/builtins.rs
@@ -1,17 +1,92 @@
-use crate::operations::OpKind;
+use crate::operations::{BinOp, OpKind};
 use crate::semantics::{
     skip_resolve_expr, typecheck, Hir, HirKind, Nir, NirKind, NzEnv, VarEnv,
 };
 use crate::syntax::map::DupTreeMap;
 use crate::syntax::Const::Type;
 use crate::syntax::{
-    BinOp, Builtin, Const, Expr, ExprKind, InterpolatedText,
-    InterpolatedTextContents, Label, NaiveDouble, NumKind, Span, UnspannedExpr,
-    V,
+    Const, Expr, ExprKind, InterpolatedText, InterpolatedTextContents, Label,
+    NaiveDouble, NumKind, Span, UnspannedExpr, V,
 };
 use std::collections::HashMap;
 use std::convert::TryInto;
 
+/// Built-ins
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub enum Builtin {
+    Bool,
+    Natural,
+    Integer,
+    Double,
+    Text,
+    List,
+    Optional,
+    OptionalNone,
+    NaturalBuild,
+    NaturalFold,
+    NaturalIsZero,
+    NaturalEven,
+    NaturalOdd,
+    NaturalToInteger,
+    NaturalShow,
+    NaturalSubtract,
+    IntegerToDouble,
+    IntegerShow,
+    IntegerNegate,
+    IntegerClamp,
+    DoubleShow,
+    ListBuild,
+    ListFold,
+    ListLength,
+    ListHead,
+    ListLast,
+    ListIndexed,
+    ListReverse,
+    OptionalFold,
+    OptionalBuild,
+    TextShow,
+}
+
+impl Builtin {
+    pub fn parse(s: &str) -> Option<Self> {
+        use Builtin::*;
+        match s {
+            "Bool" => Some(Bool),
+            "Natural" => Some(Natural),
+            "Integer" => Some(Integer),
+            "Double" => Some(Double),
+            "Text" => Some(Text),
+            "List" => Some(List),
+            "Optional" => Some(Optional),
+            "None" => Some(OptionalNone),
+            "Natural/build" => Some(NaturalBuild),
+            "Natural/fold" => Some(NaturalFold),
+            "Natural/isZero" => Some(NaturalIsZero),
+            "Natural/even" => Some(NaturalEven),
+            "Natural/odd" => Some(NaturalOdd),
+            "Natural/toInteger" => Some(NaturalToInteger),
+            "Natural/show" => Some(NaturalShow),
+            "Natural/subtract" => Some(NaturalSubtract),
+            "Integer/toDouble" => Some(IntegerToDouble),
+            "Integer/show" => Some(IntegerShow),
+            "Integer/negate" => Some(IntegerNegate),
+            "Integer/clamp" => Some(IntegerClamp),
+            "Double/show" => Some(DoubleShow),
+            "List/build" => Some(ListBuild),
+            "List/fold" => Some(ListFold),
+            "List/length" => Some(ListLength),
+            "List/head" => Some(ListHead),
+            "List/last" => Some(ListLast),
+            "List/indexed" => Some(ListIndexed),
+            "List/reverse" => Some(ListReverse),
+            "Optional/fold" => Some(OptionalFold),
+            "Optional/build" => Some(OptionalBuild),
+            "Text/show" => Some(TextShow),
+            _ => None,
+        }
+    }
+}
+
 /// A partially applied builtin.
 /// Invariant: the evaluation of the given args must not be able to progress further
 #[derive(Debug, Clone)]
@@ -492,3 +567,42 @@ impl std::cmp::PartialEq for BuiltinClosure {
     }
 }
 impl std::cmp::Eq for BuiltinClosure {}
+
+impl std::fmt::Display for Builtin {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        use Builtin::*;
+        f.write_str(match *self {
+            Bool => "Bool",
+            Natural => "Natural",
+            Integer => "Integer",
+            Double => "Double",
+            Text => "Text",
+            List => "List",
+            Optional => "Optional",
+            OptionalNone => "None",
+            NaturalBuild => "Natural/build",
+            NaturalFold => "Natural/fold",
+            NaturalIsZero => "Natural/isZero",
+            NaturalEven => "Natural/even",
+            NaturalOdd => "Natural/odd",
+            NaturalToInteger => "Natural/toInteger",
+            NaturalShow => "Natural/show",
+            NaturalSubtract => "Natural/subtract",
+            IntegerToDouble => "Integer/toDouble",
+            IntegerNegate => "Integer/negate",
+            IntegerClamp => "Integer/clamp",
+            IntegerShow => "Integer/show",
+            DoubleShow => "Double/show",
+            ListBuild => "List/build",
+            ListFold => "List/fold",
+            ListLength => "List/length",
+            ListHead => "List/head",
+            ListLast => "List/last",
+            ListIndexed => "List/indexed",
+            ListReverse => "List/reverse",
+            OptionalFold => "Optional/fold",
+            OptionalBuild => "Optional/build",
+            TextShow => "Text/show",
+        })
+    }
+}
diff --git a/dhall/src/operations.rs b/dhall/src/operations.rs
index 363cd10..1ebf288 100644
--- a/dhall/src/operations.rs
+++ b/dhall/src/operations.rs
@@ -3,15 +3,46 @@ use std::borrow::Cow;
 use std::cmp::max;
 use std::collections::HashMap;
 
+use crate::builtins::Builtin;
 use crate::error::{ErrorBuilder, TypeError};
 use crate::semantics::{
     merge_maps, mk_span_err, mkerr, ret_kind, ret_op, ret_ref, Binder, Closure,
     Hir, HirKind, Nir, NirKind, Ret, TextLit, Tir, TyEnv, Type,
 };
 use crate::syntax::map::DupTreeSet;
-use crate::syntax::{
-    trivial_result, BinOp, Builtin, Const, ExprKind, Label, NumKind, Span,
-};
+use crate::syntax::{trivial_result, Const, ExprKind, Label, NumKind, Span};
+
+// Definition order must match precedence order for
+// pretty-printing to work correctly
+#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum BinOp {
+    /// `x ? y`
+    ImportAlt,
+    /// `x || y`
+    BoolOr,
+    /// `x + y`
+    NaturalPlus,
+    /// `x ++ y`
+    TextAppend,
+    /// `x # y`
+    ListAppend,
+    /// `x && y`
+    BoolAnd,
+    /// `x ∧ y`
+    RecursiveRecordMerge,
+    /// `x ⫽ y`
+    RightBiasedRecordMerge,
+    /// `x ⩓ y`
+    RecursiveRecordTypeMerge,
+    /// `x * y`
+    NaturalTimes,
+    /// `x == y`
+    BoolEQ,
+    /// `x != y`
+    BoolNE,
+    /// x === y
+    Equivalence,
+}
 
 /// Operations
 #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
diff --git a/dhall/src/semantics/nze/nir.rs b/dhall/src/semantics/nze/nir.rs
index e2a0113..12f1b14 100644
--- a/dhall/src/semantics/nze/nir.rs
+++ b/dhall/src/semantics/nze/nir.rs
@@ -1,16 +1,15 @@
 use std::collections::HashMap;
 use std::rc::Rc;
 
-use crate::builtins::BuiltinClosure;
-use crate::operations::OpKind;
+use crate::builtins::{Builtin, BuiltinClosure};
+use crate::operations::{BinOp, OpKind};
 use crate::semantics::nze::lazy;
 use crate::semantics::{
     apply_any, normalize_hir, normalize_one_layer, squash_textlit, Binder, Hir,
     HirKind, NzEnv, NzVar, TyEnv, Type, Universe, VarEnv,
 };
 use crate::syntax::{
-    BinOp, Builtin, Const, Expr, ExprKind, InterpolatedTextContents, Label,
-    NumKind, Span,
+    Const, Expr, ExprKind, InterpolatedTextContents, Label, NumKind, Span,
 };
 use crate::ToExprOptions;
 
diff --git a/dhall/src/semantics/resolve/resolve.rs b/dhall/src/semantics/resolve/resolve.rs
index bbcd240..cd5232a 100644
--- a/dhall/src/semantics/resolve/resolve.rs
+++ b/dhall/src/semantics/resolve/resolve.rs
@@ -4,15 +4,16 @@ use std::env;
 use std::path::PathBuf;
 use url::Url;
 
+use crate::builtins::Builtin;
 use crate::error::ErrorBuilder;
 use crate::error::{Error, ImportError};
-use crate::operations::OpKind;
+use crate::operations::{BinOp, OpKind};
 use crate::semantics::{mkerr, Hir, HirKind, ImportEnv, NameEnv, Type};
 use crate::syntax;
 use crate::syntax::map::DupTreeMap;
 use crate::syntax::{
-    BinOp, Builtin, Expr, ExprKind, FilePath, FilePrefix, Hash, ImportMode,
-    ImportTarget, Span, UnspannedExpr, URL,
+    Expr, ExprKind, FilePath, FilePrefix, Hash, ImportMode, ImportTarget, Span,
+    UnspannedExpr, URL,
 };
 use crate::{Parsed, Resolved};
 
diff --git a/dhall/src/semantics/tck/tir.rs b/dhall/src/semantics/tck/tir.rs
index 89a8027..ec15a1f 100644
--- a/dhall/src/semantics/tck/tir.rs
+++ b/dhall/src/semantics/tck/tir.rs
@@ -1,6 +1,7 @@
+use crate::builtins::Builtin;
 use crate::error::{ErrorBuilder, TypeError};
 use crate::semantics::{mkerr, Hir, Nir, NirKind, NzEnv, TyEnv, VarEnv};
-use crate::syntax::{Builtin, Const, Expr, Span};
+use crate::syntax::{Const, Expr, Span};
 
 /// The type of a type. 0 is `Type`, 1 is `Kind`, etc...
 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Default)]
diff --git a/dhall/src/semantics/tck/typecheck.rs b/dhall/src/semantics/tck/typecheck.rs
index a31f15c..c6300d9 100644
--- a/dhall/src/semantics/tck/typecheck.rs
+++ b/dhall/src/semantics/tck/typecheck.rs
@@ -1,13 +1,11 @@
 use std::cmp::max;
 use std::collections::HashMap;
 
-use crate::builtins::type_of_builtin;
+use crate::builtins::{type_of_builtin, Builtin};
 use crate::error::{ErrorBuilder, TypeError, TypeMessage};
 use crate::operations::typecheck_operation;
 use crate::semantics::{Hir, HirKind, Nir, NirKind, Tir, TyEnv, Type};
-use crate::syntax::{
-    Builtin, Const, ExprKind, InterpolatedTextContents, NumKind, Span,
-};
+use crate::syntax::{Const, ExprKind, InterpolatedTextContents, NumKind, Span};
 
 fn function_check(a: Const, b: Const) -> Const {
     if b == Const::Type {
diff --git a/dhall/src/syntax/ast/expr.rs b/dhall/src/syntax/ast/expr.rs
index 62734bf..8f55540 100644
--- a/dhall/src/syntax/ast/expr.rs
+++ b/dhall/src/syntax/ast/expr.rs
@@ -1,5 +1,6 @@
 use std::collections::BTreeMap;
 
+use crate::builtins::Builtin;
 use crate::error::Error;
 use crate::operations::OpKind;
 use crate::semantics::Universe;
@@ -37,74 +38,6 @@ impl Const {
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct V(pub Label, pub usize);
 
-// Definition order must match precedence order for
-// pretty-printing to work correctly
-#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub enum BinOp {
-    /// `x ? y`
-    ImportAlt,
-    /// `x || y`
-    BoolOr,
-    /// `x + y`
-    NaturalPlus,
-    /// `x ++ y`
-    TextAppend,
-    /// `x # y`
-    ListAppend,
-    /// `x && y`
-    BoolAnd,
-    /// `x ∧ y`
-    RecursiveRecordMerge,
-    /// `x ⫽ y`
-    RightBiasedRecordMerge,
-    /// `x ⩓ y`
-    RecursiveRecordTypeMerge,
-    /// `x * y`
-    NaturalTimes,
-    /// `x == y`
-    BoolEQ,
-    /// `x != y`
-    BoolNE,
-    /// x === y
-    Equivalence,
-}
-
-/// Built-ins
-#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
-pub enum Builtin {
-    Bool,
-    Natural,
-    Integer,
-    Double,
-    Text,
-    List,
-    Optional,
-    OptionalNone,
-    NaturalBuild,
-    NaturalFold,
-    NaturalIsZero,
-    NaturalEven,
-    NaturalOdd,
-    NaturalToInteger,
-    NaturalShow,
-    NaturalSubtract,
-    IntegerToDouble,
-    IntegerShow,
-    IntegerNegate,
-    IntegerClamp,
-    DoubleShow,
-    ListBuild,
-    ListFold,
-    ListLength,
-    ListHead,
-    ListLast,
-    ListIndexed,
-    ListReverse,
-    OptionalFold,
-    OptionalBuild,
-    TextShow,
-}
-
 // Each node carries an annotation.
 #[derive(Debug, Clone)]
 pub struct Expr {
diff --git a/dhall/src/syntax/binary/decode.rs b/dhall/src/syntax/binary/decode.rs
index f062089..195bd0a 100644
--- a/dhall/src/syntax/binary/decode.rs
+++ b/dhall/src/syntax/binary/decode.rs
@@ -25,8 +25,10 @@ fn rc(x: UnspannedExpr) -> Expr {
 }
 
 fn cbor_value_to_dhall(data: &cbor::Value) -> Result<DecodedExpr, DecodeError> {
+    use crate::builtins::Builtin;
+    use crate::operations::BinOp;
     use cbor::Value::*;
-    use syntax::{BinOp, Builtin, Const};
+    use syntax::Const;
     use ExprKind::*;
     use OpKind::*;
     Ok(rc(match data {
diff --git a/dhall/src/syntax/binary/encode.rs b/dhall/src/syntax/binary/encode.rs
index cef2af8..913dd67 100644
--- a/dhall/src/syntax/binary/encode.rs
+++ b/dhall/src/syntax/binary/encode.rs
@@ -2,8 +2,9 @@ use serde_cbor::value::value as cbor;
 use std::collections::BTreeMap;
 use std::vec;
 
+use crate::builtins::Builtin;
 use crate::error::EncodeError;
-use crate::operations::OpKind;
+use crate::operations::{BinOp, OpKind};
 use crate::syntax;
 use crate::syntax::map::DupTreeMap;
 use crate::syntax::{
@@ -47,7 +48,6 @@ where
 {
     use cbor::Value::{String, I64, U64};
     use std::iter::once;
-    use syntax::Builtin;
     use syntax::ExprKind::*;
     use syntax::NumKind::*;
     use OpKind::*;
@@ -116,7 +116,7 @@ where
         SomeLit(x) => ser_seq!(ser; tag(5), null(), expr(x)),
         EmptyListLit(x) => match x.as_ref() {
             Op(App(f, a)) => match f.as_ref() {
-                ExprKind::Builtin(Builtin::List) => {
+                ExprKind::Builtin(self::Builtin::List) => {
                     ser_seq!(ser; tag(4), expr(a))
                 }
                 _ => ser_seq!(ser; tag(28), expr(x)),
@@ -138,7 +138,7 @@ where
         UnionType(map) => ser_seq!(ser; tag(11), UnionMap(map)),
         Op(Field(x, l)) => ser_seq!(ser; tag(9), expr(x), label(l)),
         Op(BinOp(op, x, y)) => {
-            use syntax::BinOp::*;
+            use self::BinOp::*;
             let op = match op {
                 BoolOr => 0,
                 BoolAnd => 1,
diff --git a/dhall/src/syntax/text/parser.rs b/dhall/src/syntax/text/parser.rs
index 8d76225..dbf5c75 100644
--- a/dhall/src/syntax/text/parser.rs
+++ b/dhall/src/syntax/text/parser.rs
@@ -36,46 +36,6 @@ enum Selector {
     ProjectionByExpr(Expr),
 }
 
-impl crate::syntax::Builtin {
-    pub fn parse(s: &str) -> Option<Self> {
-        use crate::syntax::Builtin::*;
-        match s {
-            "Bool" => Some(Bool),
-            "Natural" => Some(Natural),
-            "Integer" => Some(Integer),
-            "Double" => Some(Double),
-            "Text" => Some(Text),
-            "List" => Some(List),
-            "Optional" => Some(Optional),
-            "None" => Some(OptionalNone),
-            "Natural/build" => Some(NaturalBuild),
-            "Natural/fold" => Some(NaturalFold),
-            "Natural/isZero" => Some(NaturalIsZero),
-            "Natural/even" => Some(NaturalEven),
-            "Natural/odd" => Some(NaturalOdd),
-            "Natural/toInteger" => Some(NaturalToInteger),
-            "Natural/show" => Some(NaturalShow),
-            "Natural/subtract" => Some(NaturalSubtract),
-            "Integer/toDouble" => Some(IntegerToDouble),
-            "Integer/show" => Some(IntegerShow),
-            "Integer/negate" => Some(IntegerNegate),
-            "Integer/clamp" => Some(IntegerClamp),
-            "Double/show" => Some(DoubleShow),
-            "List/build" => Some(ListBuild),
-            "List/fold" => Some(ListFold),
-            "List/length" => Some(ListLength),
-            "List/head" => Some(ListHead),
-            "List/last" => Some(ListLast),
-            "List/indexed" => Some(ListIndexed),
-            "List/reverse" => Some(ListReverse),
-            "Optional/fold" => Some(OptionalFold),
-            "Optional/build" => Some(OptionalBuild),
-            "Text/show" => Some(TextShow),
-            _ => None,
-        }
-    }
-}
-
 fn input_to_span(input: ParseInput) -> Span {
     Span::make(input.user_data().clone(), input.as_pair().as_span())
 }
@@ -129,7 +89,7 @@ fn trim_indent(lines: &mut Vec<ParsedText>) {
 
 /// Insert the expr into the map; in case of collision, create a RecursiveRecordMerge node.
 fn insert_recordlit_entry(map: &mut BTreeMap<Label, Expr>, l: Label, e: Expr) {
-    use crate::syntax::BinOp::RecursiveRecordMerge;
+    use crate::operations::BinOp::RecursiveRecordMerge;
     use std::collections::btree_map::Entry;
     match map.entry(l) {
         Entry::Vacant(entry) => {
@@ -147,7 +107,7 @@ fn insert_recordlit_entry(map: &mut BTreeMap<Label, Expr>, l: Label, e: Expr) {
 }
 
 fn desugar_with_expr(x: Expr, labels: &[Label], y: Expr) -> Expr {
-    use crate::syntax::BinOp::RightBiasedRecordMerge;
+    use crate::operations::BinOp::RightBiasedRecordMerge;
     let expr = |k| Expr::new(k, Span::WithSugar);
     match labels {
         [] => y,
@@ -391,7 +351,7 @@ impl DhallParser {
     #[alias(expression)]
     fn builtin(input: ParseInput) -> ParseResult<Expr> {
         let s = input.as_str();
-        let e = match crate::syntax::Builtin::parse(s) {
+        let e = match crate::builtins::Builtin::parse(s) {
             Some(b) => Builtin(b),
             None => match s {
                 "True" => Num(Bool(true)),
@@ -784,7 +744,7 @@ impl DhallParser {
         op: ParseInput,
         r: Expr,
     ) -> ParseResult<Expr> {
-        use crate::syntax::BinOp::*;
+        use crate::operations::BinOp::*;
         use Rule::*;
         let op = match op.as_rule() {
             import_alt => ImportAlt,
diff --git a/dhall/src/syntax/text/printer.rs b/dhall/src/syntax/text/printer.rs
index a85f435..9e90660 100644
--- a/dhall/src/syntax/text/printer.rs
+++ b/dhall/src/syntax/text/printer.rs
@@ -1,4 +1,5 @@
-use crate::operations::OpKind;
+use crate::builtins::Builtin;
+use crate::operations::{BinOp, OpKind};
 use crate::syntax::*;
 use itertools::Itertools;
 use std::fmt::{self, Display};
@@ -15,7 +16,7 @@ enum PrintPhase {
     // `operator-expression`
     Operator,
     // All the `<operator>-expression`s
-    BinOp(ast::BinOp),
+    BinOp(self::BinOp),
     // `application-expression`
     App,
     // `import-expression`
@@ -335,7 +336,7 @@ impl Display for Const {
 
 impl Display for BinOp {
     fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
-        use crate::syntax::BinOp::*;
+        use BinOp::*;
         f.write_str(match self {
             BoolOr => "||",
             TextAppend => "++",
@@ -383,7 +384,7 @@ impl Display for Label {
         let is_reserved = match s.as_str() {
             "let" | "in" | "if" | "then" | "else" | "Type" | "Kind"
             | "Sort" | "True" | "False" | "Some" => true,
-            _ => crate::syntax::Builtin::parse(&s).is_some(),
+            _ => Builtin::parse(&s).is_some(),
         };
         if !is_reserved && s.chars().all(|c| c.is_ascii_alphanumeric()) {
             write!(f, "{}", s)
@@ -481,45 +482,6 @@ impl<SubExpr: Display> Display for Import<SubExpr> {
     }
 }
 
-impl Display for Builtin {
-    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
-        use crate::syntax::Builtin::*;
-        f.write_str(match *self {
-            Bool => "Bool",
-            Natural => "Natural",
-            Integer => "Integer",
-            Double => "Double",
-            Text => "Text",
-            List => "List",
-            Optional => "Optional",
-            OptionalNone => "None",
-            NaturalBuild => "Natural/build",
-            NaturalFold => "Natural/fold",
-            NaturalIsZero => "Natural/isZero",
-            NaturalEven => "Natural/even",
-            NaturalOdd => "Natural/odd",
-            NaturalToInteger => "Natural/toInteger",
-            NaturalShow => "Natural/show",
-            NaturalSubtract => "Natural/subtract",
-            IntegerToDouble => "Integer/toDouble",
-            IntegerNegate => "Integer/negate",
-            IntegerClamp => "Integer/clamp",
-            IntegerShow => "Integer/show",
-            DoubleShow => "Double/show",
-            ListBuild => "List/build",
-            ListFold => "List/fold",
-            ListLength => "List/length",
-            ListHead => "List/head",
-            ListLast => "List/last",
-            ListIndexed => "List/indexed",
-            ListReverse => "List/reverse",
-            OptionalFold => "Optional/fold",
-            OptionalBuild => "Optional/build",
-            TextShow => "Text/show",
-        })
-    }
-}
-
 impl Display for Scheme {
     fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
         use crate::syntax::Scheme::*;
diff --git a/serde_dhall/src/value.rs b/serde_dhall/src/value.rs
index e8f333e..03cfdba 100644
--- a/serde_dhall/src/value.rs
+++ b/serde_dhall/src/value.rs
@@ -1,8 +1,9 @@
 use std::collections::{BTreeMap, HashMap};
 
+use dhall::builtins::Builtin;
 use dhall::operations::OpKind;
 use dhall::semantics::{Hir, HirKind, Nir, NirKind};
-use dhall::syntax::{Builtin, Expr, ExprKind, NumKind, Span};
+use dhall::syntax::{Expr, ExprKind, NumKind, Span};
 
 use crate::{Error, ErrorKind, FromDhall, Result, Sealed};
 
-- 
cgit v1.3.1


From 092b7208ffd22f8facc7af387ac307e59208d52c Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Tue, 7 Apr 2020 11:19:36 +0100
Subject: Move duplicate field checking to parser

---
 dhall/src/builtins.rs                              |   8 +-
 dhall/src/operations.rs                            |  13 +-
 dhall/src/semantics/resolve/resolve.rs             |   4 +-
 dhall/src/semantics/tck/typecheck.rs               |  61 ++---
 dhall/src/syntax/ast/expr.rs                       |   5 +-
 dhall/src/syntax/ast/map.rs                        | 282 ---------------------
 dhall/src/syntax/ast/mod.rs                        |   1 -
 dhall/src/syntax/binary/encode.rs                  |  13 +-
 dhall/src/syntax/text/parser.rs                    |  64 ++++-
 dhall/tests/type-inference/failure/mixedUnions.txt |   6 +-
 .../tests/type-inference/failure/recordOfKind.txt  |   4 +-
 .../failure/unit/RecordMixedKinds3.txt             |   4 +-
 .../unit/RecordProjectionDuplicateFields.txt       |   8 +-
 .../failure/unit/RecordTypeDuplicateFields.txt     |   8 +-
 .../failure/unit/RecordTypeValueMember.txt         |   4 +-
 .../unit/RightBiasedRecordMergeMixedKinds2.txt     |   4 +-
 .../unit/RightBiasedRecordMergeMixedKinds3.txt     |   4 +-
 .../failure/unit/UnionTypeDuplicateVariants1.txt   |   8 +-
 .../failure/unit/UnionTypeDuplicateVariants2.txt   |   8 +-
 .../failure/unit/UnionTypeMixedKinds.txt           |   6 +-
 .../failure/unit/UnionTypeMixedKinds2.txt          |   6 +-
 .../failure/unit/UnionTypeMixedKinds3.txt          |   6 +-
 .../failure/unit/UnionTypeNotType.txt              |   6 +-
 tests_buffer                                       |   1 +
 24 files changed, 132 insertions(+), 402 deletions(-)
 delete mode 100644 dhall/src/syntax/ast/map.rs

(limited to 'dhall/src/semantics/resolve')

diff --git a/dhall/src/builtins.rs b/dhall/src/builtins.rs
index bb8173c..67929a0 100644
--- a/dhall/src/builtins.rs
+++ b/dhall/src/builtins.rs
@@ -1,15 +1,15 @@
+use std::collections::{BTreeMap, HashMap};
+use std::convert::TryInto;
+
 use crate::operations::{BinOp, OpKind};
 use crate::semantics::{
     skip_resolve_expr, typecheck, Hir, HirKind, Nir, NirKind, NzEnv, VarEnv,
 };
-use crate::syntax::map::DupTreeMap;
 use crate::syntax::Const::Type;
 use crate::syntax::{
     Const, Expr, ExprKind, InterpolatedText, InterpolatedTextContents, Label,
     NaiveDouble, NumKind, Span, UnspannedExpr, V,
 };
-use std::collections::HashMap;
-use std::convert::TryInto;
 
 /// Built-ins
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
@@ -147,7 +147,7 @@ macro_rules! make_type {
         )))
     };
     ({ $($label:ident : $ty:ident),* }) => {{
-        let mut kts = DupTreeMap::new();
+        let mut kts = BTreeMap::new();
         $(
             kts.insert(
                 Label::from(stringify!($label)),
diff --git a/dhall/src/operations.rs b/dhall/src/operations.rs
index 1ebf288..8b5fa10 100644
--- a/dhall/src/operations.rs
+++ b/dhall/src/operations.rs
@@ -1,7 +1,7 @@
 use itertools::Itertools;
 use std::borrow::Cow;
 use std::cmp::max;
-use std::collections::HashMap;
+use std::collections::{BTreeSet, HashMap};
 
 use crate::builtins::Builtin;
 use crate::error::{ErrorBuilder, TypeError};
@@ -9,7 +9,6 @@ use crate::semantics::{
     merge_maps, mk_span_err, mkerr, ret_kind, ret_op, ret_ref, Binder, Closure,
     Hir, HirKind, Nir, NirKind, Ret, TextLit, Tir, TyEnv, Type,
 };
-use crate::syntax::map::DupTreeSet;
 use crate::syntax::{trivial_result, Const, ExprKind, Label, NumKind, Span};
 
 // Definition order must match precedence order for
@@ -60,7 +59,7 @@ pub enum OpKind<SubExpr> {
     ///  `e.x`
     Field(SubExpr, Label),
     ///  `e.{ x, y, z }`
-    Projection(SubExpr, DupTreeSet<Label>),
+    Projection(SubExpr, BTreeSet<Label>),
     ///  `e.(t)`
     ProjectionByExpr(SubExpr, SubExpr),
     ///  `x::y`
@@ -565,13 +564,7 @@ pub fn typecheck_operation(
                 match kts.get(l) {
                     None => return span_err("ProjectionMissingEntry"),
                     Some(t) => {
-                        use std::collections::hash_map::Entry;
-                        match new_kts.entry(l.clone()) {
-                            Entry::Occupied(_) => {
-                                return span_err("ProjectionDuplicateField")
-                            }
-                            Entry::Vacant(e) => e.insert(t.clone()),
-                        }
+                        new_kts.insert(l.clone(), t.clone());
                     }
                 };
             }
diff --git a/dhall/src/semantics/resolve/resolve.rs b/dhall/src/semantics/resolve/resolve.rs
index cd5232a..e96f16b 100644
--- a/dhall/src/semantics/resolve/resolve.rs
+++ b/dhall/src/semantics/resolve/resolve.rs
@@ -1,5 +1,6 @@
 use itertools::Itertools;
 use std::borrow::Cow;
+use std::collections::BTreeMap;
 use std::env;
 use std::path::PathBuf;
 use url::Url;
@@ -10,7 +11,6 @@ use crate::error::{Error, ImportError};
 use crate::operations::{BinOp, OpKind};
 use crate::semantics::{mkerr, Hir, HirKind, ImportEnv, NameEnv, Type};
 use crate::syntax;
-use crate::syntax::map::DupTreeMap;
 use crate::syntax::{
     Expr, ExprKind, FilePath, FilePrefix, Hash, ImportMode, ImportTarget, Span,
     UnspannedExpr, URL,
@@ -199,7 +199,7 @@ fn mkexpr(kind: UnspannedExpr) -> Expr {
 
 fn make_aslocation_uniontype() -> Expr {
     let text_type = mkexpr(ExprKind::Builtin(Builtin::Text));
-    let mut union = DupTreeMap::default();
+    let mut union = BTreeMap::default();
     union.insert("Local".into(), Some(text_type.clone()));
     union.insert("Remote".into(), Some(text_type.clone()));
     union.insert("Environment".into(), Some(text_type));
diff --git a/dhall/src/semantics/tck/typecheck.rs b/dhall/src/semantics/tck/typecheck.rs
index c6300d9..45a3055 100644
--- a/dhall/src/semantics/tck/typecheck.rs
+++ b/dhall/src/semantics/tck/typecheck.rs
@@ -1,5 +1,4 @@
 use std::cmp::max;
-use std::collections::HashMap;
 
 use crate::builtins::{type_of_builtin, Builtin};
 use crate::error::{ErrorBuilder, TypeError, TypeMessage};
@@ -107,71 +106,55 @@ fn type_one_layer(
             Nir::from_builtin(Builtin::List).app(t).to_type(Const::Type)
         }
         ExprKind::RecordLit(kvs) => {
-            use std::collections::hash_map::Entry;
-            let mut kts = HashMap::new();
             // An empty record type has type Type
             let mut k = Const::Type;
-            for (x, v) in kvs {
-                // Check for duplicated entries
-                match kts.entry(x.clone()) {
-                    Entry::Occupied(_) => {
-                        return span_err("RecordTypeDuplicateField")
-                    }
-                    Entry::Vacant(e) => e.insert(v.ty().to_nir()),
-                };
-
+            for (_, v) in kvs {
                 // Check that the fields have a valid kind
                 match v.ty().ty().as_const() {
                     Some(c) => k = max(k, c),
-                    None => return span_err("InvalidFieldType"),
+                    None => return mk_span_err(v.span(), "InvalidFieldType"),
                 }
             }
 
+            let kts = kvs
+                .iter()
+                .map(|(x, v)| (x.clone(), v.ty().to_nir()))
+                .collect();
+
             Nir::from_kind(NirKind::RecordType(kts)).to_type(k)
         }
         ExprKind::RecordType(kts) => {
-            use std::collections::hash_map::Entry;
-            let mut seen_fields = HashMap::new();
             // An empty record type has type Type
             let mut k = Const::Type;
-
-            for (x, t) in kts {
-                // Check for duplicated entries
-                match seen_fields.entry(x.clone()) {
-                    Entry::Occupied(_) => {
-                        return span_err("RecordTypeDuplicateField")
-                    }
-                    Entry::Vacant(e) => e.insert(()),
-                };
-
+            for (_, t) in kts {
                 // Check the type is a Const and compute final type
                 match t.ty().as_const() {
                     Some(c) => k = max(k, c),
-                    None => return span_err("InvalidFieldType"),
+                    None => return mk_span_err(t.span(), "InvalidFieldType"),
                 }
             }
 
             Type::from_const(k)
         }
         ExprKind::UnionType(kts) => {
-            use std::collections::hash_map::Entry;
-            let mut seen_fields = HashMap::new();
             // Check that all types are the same const
             let mut k = None;
-            for (x, t) in kts {
+            for (_, t) in kts {
                 if let Some(t) = t {
-                    match (k, t.ty().as_const()) {
-                        (None, Some(k2)) => k = Some(k2),
-                        (Some(k1), Some(k2)) if k1 == k2 => {}
-                        _ => return span_err("InvalidFieldType"),
+                    let c = match t.ty().as_const() {
+                        Some(c) => c,
+                        None => {
+                            return mk_span_err(t.span(), "InvalidVariantType")
+                        }
+                    };
+                    match k {
+                        None => k = Some(c),
+                        Some(k) if k == c => {}
+                        _ => {
+                            return mk_span_err(t.span(), "InvalidVariantType")
+                        }
                     }
                 }
-                match seen_fields.entry(x) {
-                    Entry::Occupied(_) => {
-                        return span_err("UnionTypeDuplicateField")
-                    }
-                    Entry::Vacant(e) => e.insert(()),
-                };
             }
 
             // An empty union type has type Type;
diff --git a/dhall/src/syntax/ast/expr.rs b/dhall/src/syntax/ast/expr.rs
index 8f55540..9d216a7 100644
--- a/dhall/src/syntax/ast/expr.rs
+++ b/dhall/src/syntax/ast/expr.rs
@@ -4,7 +4,6 @@ use crate::builtins::Builtin;
 use crate::error::Error;
 use crate::operations::OpKind;
 use crate::semantics::Universe;
-use crate::syntax::map::DupTreeMap;
 use crate::syntax::visitor;
 use crate::syntax::*;
 
@@ -81,11 +80,11 @@ pub enum ExprKind<SubExpr> {
     ///  `[x, y, z]`
     NEListLit(Vec<SubExpr>),
     ///  `{ k1 : t1, k2 : t1 }`
-    RecordType(DupTreeMap<Label, SubExpr>),
+    RecordType(BTreeMap<Label, SubExpr>),
     ///  `{ k1 = v1, k2 = v2 }`
     RecordLit(BTreeMap<Label, SubExpr>),
     ///  `< k1 : t1, k2 >`
-    UnionType(DupTreeMap<Label, Option<SubExpr>>),
+    UnionType(BTreeMap<Label, Option<SubExpr>>),
 
     ///  `x`, `x@n`
     Var(V),
diff --git a/dhall/src/syntax/ast/map.rs b/dhall/src/syntax/ast/map.rs
deleted file mode 100644
index 7a88204..0000000
--- a/dhall/src/syntax/ast/map.rs
+++ /dev/null
@@ -1,282 +0,0 @@
-/// A sorted map that allows multiple values for each key.
-pub use dup_tree_map::DupTreeMap;
-pub use dup_tree_set::DupTreeSet;
-
-mod known_size_iter {
-    pub struct KnownSizeIterator<I> {
-        pub iter: I,
-        pub size: usize,
-    }
-
-    impl<I: Iterator> Iterator for KnownSizeIterator<I> {
-        type Item = I::Item;
-
-        fn next(&mut self) -> Option<Self::Item> {
-            let next = self.iter.next();
-            if next.is_some() {
-                self.size -= 1;
-            }
-            next
-        }
-
-        fn size_hint(&self) -> (usize, Option<usize>) {
-            (self.size, Some(self.size))
-        }
-    }
-
-    // unsafe impl<I: Iterator> iter::TrustedLen for KnownSizeIterator<I> {}
-}
-
-mod tuple {
-    mod sealed {
-        pub trait Sealed {}
-    }
-    pub trait Tuple: sealed::Sealed {
-        type First;
-        type Second;
-    }
-    impl<A, B> sealed::Sealed for (A, B) {}
-    impl<A, B> Tuple for (A, B) {
-        type First = A;
-        type Second = B;
-    }
-}
-
-mod dup_tree_map {
-    use super::known_size_iter::KnownSizeIterator;
-    use super::tuple::Tuple;
-    use smallvec::SmallVec;
-    use std::collections::BTreeMap;
-    use std::iter;
-
-    type OneOrMore<V> = SmallVec<[V; 1]>;
-    type DupTreeMapInternal<K, V> = BTreeMap<K, OneOrMore<V>>;
-
-    #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
-    pub struct DupTreeMap<K, V> {
-        map: DupTreeMapInternal<K, V>,
-        size: usize,
-    }
-
-    // Generic types and functions to construct the iterators for this struct.
-    type ZipRepeatIter<T> = iter::Zip<
-        iter::Repeat<<T as Tuple>::First>,
-        <<T as Tuple>::Second as IntoIterator>::IntoIter,
-    >;
-    type DupTreeMapIter<M> = KnownSizeIterator<
-        iter::FlatMap<
-            <M as IntoIterator>::IntoIter,
-            ZipRepeatIter<<M as IntoIterator>::Item>,
-            fn(
-                <M as IntoIterator>::Item,
-            ) -> ZipRepeatIter<<M as IntoIterator>::Item>,
-        >,
-    >;
-
-    fn zip_repeat<K, I>((k, iter): (K, I)) -> ZipRepeatIter<(K, I)>
-    where
-        K: Clone,
-        I: IntoIterator,
-    {
-        iter::repeat(k).zip(iter.into_iter())
-    }
-
-    fn make_map_iter<M, K, I>(map: M, size: usize) -> DupTreeMapIter<M>
-    where
-        M: IntoIterator<Item = (K, I)>,
-        K: Clone,
-        I: IntoIterator,
-    {
-        KnownSizeIterator {
-            iter: map.into_iter().flat_map(zip_repeat),
-            size,
-        }
-    }
-
-    pub type IterMut<'a, K, V> =
-        DupTreeMapIter<&'a mut DupTreeMapInternal<K, V>>;
-    pub type Iter<'a, K, V> = DupTreeMapIter<&'a DupTreeMapInternal<K, V>>;
-    pub type IntoIter<K, V> = DupTreeMapIter<DupTreeMapInternal<K, V>>;
-
-    impl<K: Ord, V> DupTreeMap<K, V> {
-        pub fn new() -> Self {
-            DupTreeMap {
-                map: BTreeMap::new(),
-                size: 0,
-            }
-        }
-
-        pub fn insert(&mut self, key: K, value: V) {
-            self.map.entry(key).or_default().push(value);
-            self.size += 1;
-        }
-
-        pub fn len(&self) -> usize {
-            self.size
-        }
-        pub fn is_empty(&self) -> bool {
-            self.size == 0
-        }
-
-        pub fn iter(&self) -> Iter<'_, K, V> {
-            make_map_iter(&self.map, self.size)
-        }
-
-        pub fn iter_mut(&mut self) -> IterMut<'_, K, V> {
-            make_map_iter(&mut self.map, self.size)
-        }
-    }
-
-    impl<K, V> Default for DupTreeMap<K, V>
-    where
-        K: Ord,
-    {
-        fn default() -> Self {
-            Self::new()
-        }
-    }
-
-    impl<K, V> IntoIterator for DupTreeMap<K, V>
-    where
-        K: Ord + Clone,
-    {
-        type Item = (K, V);
-        type IntoIter = IntoIter<K, V>;
-
-        fn into_iter(self) -> Self::IntoIter {
-            make_map_iter(self.map, self.size)
-        }
-    }
-
-    impl<'a, K, V> IntoIterator for &'a DupTreeMap<K, V>
-    where
-        K: Ord + 'a,
-        V: 'a,
-    {
-        type Item = (&'a K, &'a V);
-        type IntoIter = Iter<'a, K, V>;
-
-        fn into_iter(self) -> Self::IntoIter {
-            self.iter()
-        }
-    }
-
-    impl<'a, K, V> IntoIterator for &'a mut DupTreeMap<K, V>
-    where
-        K: Ord + 'a,
-        V: 'a,
-    {
-        type Item = (&'a K, &'a mut V);
-        type IntoIter = IterMut<'a, K, V>;
-
-        fn into_iter(self) -> Self::IntoIter {
-            self.iter_mut()
-        }
-    }
-
-    impl<K, V> iter::FromIterator<(K, V)> for DupTreeMap<K, V>
-    where
-        K: Ord,
-    {
-        fn from_iter<T>(iter: T) -> Self
-        where
-            T: IntoIterator<Item = (K, V)>,
-        {
-            let mut map = DupTreeMap::new();
-            for (k, v) in iter {
-                map.insert(k, v);
-            }
-            map
-        }
-    }
-}
-
-mod dup_tree_set {
-    use super::tuple::Tuple;
-    use super::DupTreeMap;
-    use std::iter;
-
-    #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
-    pub struct DupTreeSet<K> {
-        map: DupTreeMap<K, ()>,
-    }
-
-    type DupTreeSetIter<M> = iter::Map<
-        <M as IntoIterator>::IntoIter,
-        fn(
-            <M as IntoIterator>::Item,
-        ) -> <<M as IntoIterator>::Item as Tuple>::First,
-    >;
-
-    pub type Iter<'a, K> = DupTreeSetIter<&'a DupTreeMap<K, ()>>;
-    pub type IntoIter<K> = DupTreeSetIter<DupTreeMap<K, ()>>;
-
-    fn drop_second<A, B>((a, _): (A, B)) -> A {
-        a
-    }
-
-    impl<K: Ord> DupTreeSet<K> {
-        pub fn new() -> Self {
-            DupTreeSet {
-                map: DupTreeMap::new(),
-            }
-        }
-
-        pub fn len(&self) -> usize {
-            self.map.len()
-        }
-        pub fn is_empty(&self) -> bool {
-            self.map.is_empty()
-        }
-
-        pub fn iter(&self) -> Iter<'_, K> {
-            self.map.iter().map(drop_second)
-        }
-    }
-
-    impl<K> Default for DupTreeSet<K>
-    where
-        K: Ord,
-    {
-        fn default() -> Self {
-            Self::new()
-        }
-    }
-
-    impl<K> IntoIterator for DupTreeSet<K>
-    where
-        K: Ord + Clone,
-    {
-        type Item = K;
-        type IntoIter = IntoIter<K>;
-
-        fn into_iter(self) -> Self::IntoIter {
-            self.map.into_iter().map(drop_second)
-        }
-    }
-
-    impl<'a, K> IntoIterator for &'a DupTreeSet<K>
-    where
-        K: Ord + 'a,
-    {
-        type Item = &'a K;
-        type IntoIter = Iter<'a, K>;
-
-        fn into_iter(self) -> Self::IntoIter {
-            self.iter()
-        }
-    }
-
-    impl<K> iter::FromIterator<K> for DupTreeSet<K>
-    where
-        K: Ord,
-    {
-        fn from_iter<T>(iter: T) -> Self
-        where
-            T: IntoIterator<Item = K>,
-        {
-            let map = iter.into_iter().map(|k| (k, ())).collect();
-            DupTreeSet { map }
-        }
-    }
-}
diff --git a/dhall/src/syntax/ast/mod.rs b/dhall/src/syntax/ast/mod.rs
index 1950154..c341af7 100644
--- a/dhall/src/syntax/ast/mod.rs
+++ b/dhall/src/syntax/ast/mod.rs
@@ -8,5 +8,4 @@ mod span;
 pub use span::*;
 mod text;
 pub use text::*;
-pub mod map;
 pub mod visitor;
diff --git a/dhall/src/syntax/binary/encode.rs b/dhall/src/syntax/binary/encode.rs
index 913dd67..b6bbabe 100644
--- a/dhall/src/syntax/binary/encode.rs
+++ b/dhall/src/syntax/binary/encode.rs
@@ -6,7 +6,6 @@ use crate::builtins::Builtin;
 use crate::error::EncodeError;
 use crate::operations::{BinOp, OpKind};
 use crate::syntax;
-use crate::syntax::map::DupTreeMap;
 use crate::syntax::{
     Expr, ExprKind, FilePrefix, Hash, Import, ImportMode, ImportTarget, Label,
     Scheme, V,
@@ -21,8 +20,7 @@ enum Serialize<'a> {
     Expr(&'a Expr),
     CBOR(cbor::Value),
     RecordMap(&'a BTreeMap<Label, Expr>),
-    RecordDupMap(&'a DupTreeMap<Label, Expr>),
-    UnionMap(&'a DupTreeMap<Label, Option<Expr>>),
+    UnionMap(&'a BTreeMap<Label, Option<Expr>>),
 }
 
 macro_rules! count {
@@ -52,7 +50,7 @@ where
     use syntax::NumKind::*;
     use OpKind::*;
 
-    use self::Serialize::{RecordDupMap, RecordMap, UnionMap};
+    use self::Serialize::{RecordMap, UnionMap};
     fn expr(x: &Expr) -> self::Serialize<'_> {
         self::Serialize::Expr(x)
     }
@@ -133,7 +131,7 @@ where
                 Text(x) => cbor(String(x)),
             })))
         }
-        RecordType(map) => ser_seq!(ser; tag(7), RecordDupMap(map)),
+        RecordType(map) => ser_seq!(ser; tag(7), RecordMap(map)),
         RecordLit(map) => ser_seq!(ser; tag(8), RecordMap(map)),
         UnionType(map) => ser_seq!(ser; tag(11), UnionMap(map)),
         Op(Field(x, l)) => ser_seq!(ser; tag(9), expr(x), label(l)),
@@ -266,11 +264,6 @@ impl<'a> serde::ser::Serialize for Serialize<'a> {
         match self {
             Serialize::Expr(e) => serialize_subexpr(ser, e),
             Serialize::CBOR(v) => v.serialize(ser),
-            Serialize::RecordDupMap(map) => {
-                ser.collect_map(map.iter().map(|(k, v)| {
-                    (cbor::Value::String(k.into()), Serialize::Expr(v))
-                }))
-            }
             Serialize::RecordMap(map) => {
                 ser.collect_map(map.iter().map(|(k, v)| {
                     (cbor::Value::String(k.into()), Serialize::Expr(v))
diff --git a/dhall/src/syntax/text/parser.rs b/dhall/src/syntax/text/parser.rs
index dbf5c75..dcaf5e4 100644
--- a/dhall/src/syntax/text/parser.rs
+++ b/dhall/src/syntax/text/parser.rs
@@ -1,14 +1,13 @@
 use itertools::Itertools;
 use pest::prec_climber as pcl;
 use pest::prec_climber::PrecClimber;
-use std::collections::BTreeMap;
+use std::collections::{BTreeMap, BTreeSet};
 use std::iter::once;
 use std::rc::Rc;
 
 use pest_consume::{match_nodes, Parser};
 
 use crate::operations::OpKind::*;
-use crate::syntax::map::{DupTreeMap, DupTreeSet};
 use crate::syntax::ExprKind::*;
 use crate::syntax::NumKind::*;
 use crate::syntax::{
@@ -32,7 +31,7 @@ pub type ParseResult<T> = Result<T, ParseError>;
 #[derive(Debug)]
 enum Selector {
     Field(Label),
-    Projection(DupTreeSet<Label>),
+    Projection(BTreeSet<Label>),
     ProjectionByExpr(Expr),
 }
 
@@ -879,9 +878,20 @@ impl DhallParser {
         Ok((stor, input_to_span(input)))
     }
 
-    fn labels(input: ParseInput) -> ParseResult<DupTreeSet<Label>> {
-        Ok(match_nodes!(input.into_children();
-            [label(ls)..] => ls.collect(),
+    fn labels(input: ParseInput) -> ParseResult<BTreeSet<Label>> {
+        Ok(match_nodes!(input.children();
+            [label(ls)..] => {
+                let mut set = BTreeSet::default();
+                for l in ls {
+                    if set.contains(&l) {
+                        return Err(
+                            input.error(format!("Duplicate field in projection"))
+                        )
+                    }
+                    set.insert(l);
+                }
+                set
+            },
         ))
     }
 
@@ -921,9 +931,26 @@ impl DhallParser {
 
     fn non_empty_record_type(
         input: ParseInput,
-    ) -> ParseResult<DupTreeMap<Label, Expr>> {
-        Ok(match_nodes!(input.into_children();
-            [record_type_entry(entries)..] => entries.collect()
+    ) -> ParseResult<BTreeMap<Label, Expr>> {
+        Ok(match_nodes!(input.children();
+            [record_type_entry(entries)..] => {
+                let mut map = BTreeMap::default();
+                for (l, t) in entries {
+                    use std::collections::btree_map::Entry;
+                    match map.entry(l) {
+                        Entry::Occupied(_) => {
+                            return Err(input.error(
+                                "Duplicate field in record type"
+                                    .to_string(),
+                            ));
+                        }
+                        Entry::Vacant(e) => {
+                            e.insert(t);
+                        }
+                    }
+                }
+                map
+            },
         ))
     }
 
@@ -972,7 +999,24 @@ impl DhallParser {
     fn union_type(input: ParseInput) -> ParseResult<UnspannedExpr> {
         let map = match_nodes!(input.children();
             [empty_union_type(_)] => Default::default(),
-            [union_type_entry(entries)..] => entries.collect(),
+            [union_type_entry(entries)..] => {
+                let mut map = BTreeMap::default();
+                for (l, t) in entries {
+                    use std::collections::btree_map::Entry;
+                    match map.entry(l) {
+                        Entry::Occupied(_) => {
+                            return Err(input.error(
+                                "Duplicate variant in union type"
+                                    .to_string(),
+                            ));
+                        }
+                        Entry::Vacant(e) => {
+                            e.insert(t);
+                        }
+                    }
+                }
+                map
+            },
         );
         Ok(UnionType(map))
     }
diff --git a/dhall/tests/type-inference/failure/mixedUnions.txt b/dhall/tests/type-inference/failure/mixedUnions.txt
index a6ca913..2b307d0 100644
--- a/dhall/tests/type-inference/failure/mixedUnions.txt
+++ b/dhall/tests/type-inference/failure/mixedUnions.txt
@@ -1,6 +1,6 @@
-Type error: error: InvalidFieldType
- --> <current file>:1:1
+Type error: error: InvalidVariantType
+ --> <current file>:1:28
   |
 1 | < Left : Natural | Right : Type >
-  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ InvalidFieldType
+  |                            ^^^^ InvalidVariantType
   |
diff --git a/dhall/tests/type-inference/failure/recordOfKind.txt b/dhall/tests/type-inference/failure/recordOfKind.txt
index 7dcbe4f..9a243c3 100644
--- a/dhall/tests/type-inference/failure/recordOfKind.txt
+++ b/dhall/tests/type-inference/failure/recordOfKind.txt
@@ -1,6 +1,6 @@
 Type error: error: InvalidFieldType
- --> <current file>:1:1
+ --> <current file>:1:7
   |
 1 | { a = Kind }
-  | ^^^^^^^^^^^^ InvalidFieldType
+  |       ^^^^ InvalidFieldType
   |
diff --git a/dhall/tests/type-inference/failure/unit/RecordMixedKinds3.txt b/dhall/tests/type-inference/failure/unit/RecordMixedKinds3.txt
index fa8b153..a83bb4f 100644
--- a/dhall/tests/type-inference/failure/unit/RecordMixedKinds3.txt
+++ b/dhall/tests/type-inference/failure/unit/RecordMixedKinds3.txt
@@ -1,6 +1,6 @@
 Type error: error: InvalidFieldType
- --> <current file>:1:1
+ --> <current file>:1:17
   |
 1 | { x = Type, y = Kind }
-  | ^^^^^^^^^^^^^^^^^^^^^^ InvalidFieldType
+  |                 ^^^^ InvalidFieldType
   |
diff --git a/dhall/tests/type-inference/failure/unit/RecordProjectionDuplicateFields.txt b/dhall/tests/type-inference/failure/unit/RecordProjectionDuplicateFields.txt
index 05c3eed..7b35481 100644
--- a/dhall/tests/type-inference/failure/unit/RecordProjectionDuplicateFields.txt
+++ b/dhall/tests/type-inference/failure/unit/RecordProjectionDuplicateFields.txt
@@ -1,6 +1,6 @@
-Type error: error: ProjectionDuplicateField
- --> <current file>:1:1
+ --> 1:11
   |
-1 | { x = 1 }.{ x, x }
-  | ^^^^^^^^^^^^^^^^^^ ProjectionDuplicateField
+1 | { x = 1 }.{ x, x }␊
+  |           ^------^
   |
+  = Duplicate field in projection
diff --git a/dhall/tests/type-inference/failure/unit/RecordTypeDuplicateFields.txt b/dhall/tests/type-inference/failure/unit/RecordTypeDuplicateFields.txt
index d8bec44..aced8a9 100644
--- a/dhall/tests/type-inference/failure/unit/RecordTypeDuplicateFields.txt
+++ b/dhall/tests/type-inference/failure/unit/RecordTypeDuplicateFields.txt
@@ -1,6 +1,6 @@
-Type error: error: RecordTypeDuplicateField
- --> <current file>:1:1
+ --> 1:3
   |
-1 | { x: Natural, x: Natural }
-  | ^^^^^^^^^^^^^^^^^^^^^^^^^^ RecordTypeDuplicateField
+1 | { x: Natural, x: Natural }␊
+  |   ^--------------------^
   |
+  = Duplicate field in record type
diff --git a/dhall/tests/type-inference/failure/unit/RecordTypeValueMember.txt b/dhall/tests/type-inference/failure/unit/RecordTypeValueMember.txt
index 81815a2..c6c274c 100644
--- a/dhall/tests/type-inference/failure/unit/RecordTypeValueMember.txt
+++ b/dhall/tests/type-inference/failure/unit/RecordTypeValueMember.txt
@@ -1,6 +1,6 @@
 Type error: error: InvalidFieldType
- --> <current file>:1:1
+ --> <current file>:1:7
   |
 1 | { x : True }
-  | ^^^^^^^^^^^^ InvalidFieldType
+  |       ^^^^ InvalidFieldType
   |
diff --git a/dhall/tests/type-inference/failure/unit/RightBiasedRecordMergeMixedKinds2.txt b/dhall/tests/type-inference/failure/unit/RightBiasedRecordMergeMixedKinds2.txt
index 146bf7f..6a6da80 100644
--- a/dhall/tests/type-inference/failure/unit/RightBiasedRecordMergeMixedKinds2.txt
+++ b/dhall/tests/type-inference/failure/unit/RightBiasedRecordMergeMixedKinds2.txt
@@ -1,6 +1,6 @@
 Type error: error: InvalidFieldType
- --> <current file>:1:16
+ --> <current file>:1:22
   |
 1 | { x = Bool } ⫽ { x = Kind }
-  |                ^^^^^^^^^^^^ InvalidFieldType
+  |                      ^^^^ InvalidFieldType
   |
diff --git a/dhall/tests/type-inference/failure/unit/RightBiasedRecordMergeMixedKinds3.txt b/dhall/tests/type-inference/failure/unit/RightBiasedRecordMergeMixedKinds3.txt
index 71914e1..322e7f4 100644
--- a/dhall/tests/type-inference/failure/unit/RightBiasedRecordMergeMixedKinds3.txt
+++ b/dhall/tests/type-inference/failure/unit/RightBiasedRecordMergeMixedKinds3.txt
@@ -1,6 +1,6 @@
 Type error: error: InvalidFieldType
- --> <current file>:1:15
+ --> <current file>:1:21
   |
 1 | { x = {=} } ⫽ { x = Kind }
-  |               ^^^^^^^^^^^^ InvalidFieldType
+  |                     ^^^^ InvalidFieldType
   |
diff --git a/dhall/tests/type-inference/failure/unit/UnionTypeDuplicateVariants1.txt b/dhall/tests/type-inference/failure/unit/UnionTypeDuplicateVariants1.txt
index 84bfe4d..9984693 100644
--- a/dhall/tests/type-inference/failure/unit/UnionTypeDuplicateVariants1.txt
+++ b/dhall/tests/type-inference/failure/unit/UnionTypeDuplicateVariants1.txt
@@ -1,6 +1,6 @@
-Type error: error: UnionTypeDuplicateField
- --> <current file>:1:1
+ --> 1:2
   |
-1 | <x | x>
-  | ^^^^^^^ UnionTypeDuplicateField
+1 | <x | x>␊
+  |  ^---^
   |
+  = Duplicate variant in union type
diff --git a/dhall/tests/type-inference/failure/unit/UnionTypeDuplicateVariants2.txt b/dhall/tests/type-inference/failure/unit/UnionTypeDuplicateVariants2.txt
index eb20b12..fdf6dc0 100644
--- a/dhall/tests/type-inference/failure/unit/UnionTypeDuplicateVariants2.txt
+++ b/dhall/tests/type-inference/failure/unit/UnionTypeDuplicateVariants2.txt
@@ -1,6 +1,6 @@
-Type error: error: UnionTypeDuplicateField
- --> <current file>:1:1
+ --> 1:2
   |
-1 | <x | x: Natural>
-  | ^^^^^^^^^^^^^^^^ UnionTypeDuplicateField
+1 | <x | x: Natural>␊
+  |  ^------------^
   |
+  = Duplicate variant in union type
diff --git a/dhall/tests/type-inference/failure/unit/UnionTypeMixedKinds.txt b/dhall/tests/type-inference/failure/unit/UnionTypeMixedKinds.txt
index 44ce7a3..ae6c845 100644
--- a/dhall/tests/type-inference/failure/unit/UnionTypeMixedKinds.txt
+++ b/dhall/tests/type-inference/failure/unit/UnionTypeMixedKinds.txt
@@ -1,6 +1,6 @@
-Type error: error: InvalidFieldType
- --> <current file>:1:1
+Type error: error: InvalidVariantType
+ --> <current file>:1:18
   |
 1 | < x : Bool | y : Type >
-  | ^^^^^^^^^^^^^^^^^^^^^^^ InvalidFieldType
+  |                  ^^^^ InvalidVariantType
   |
diff --git a/dhall/tests/type-inference/failure/unit/UnionTypeMixedKinds2.txt b/dhall/tests/type-inference/failure/unit/UnionTypeMixedKinds2.txt
index 01f706d..faf81a9 100644
--- a/dhall/tests/type-inference/failure/unit/UnionTypeMixedKinds2.txt
+++ b/dhall/tests/type-inference/failure/unit/UnionTypeMixedKinds2.txt
@@ -1,6 +1,6 @@
-Type error: error: InvalidFieldType
- --> <current file>:1:1
+Type error: error: InvalidVariantType
+ --> <current file>:1:18
   |
 1 | < x : Kind | y : Type >
-  | ^^^^^^^^^^^^^^^^^^^^^^^ InvalidFieldType
+  |                  ^^^^ InvalidVariantType
   |
diff --git a/dhall/tests/type-inference/failure/unit/UnionTypeMixedKinds3.txt b/dhall/tests/type-inference/failure/unit/UnionTypeMixedKinds3.txt
index 496462d..bbfb1f3 100644
--- a/dhall/tests/type-inference/failure/unit/UnionTypeMixedKinds3.txt
+++ b/dhall/tests/type-inference/failure/unit/UnionTypeMixedKinds3.txt
@@ -1,6 +1,6 @@
-Type error: error: InvalidFieldType
- --> <current file>:1:1
+Type error: error: InvalidVariantType
+ --> <current file>:1:18
   |
 1 | < x : Kind | y : Bool >
-  | ^^^^^^^^^^^^^^^^^^^^^^^ InvalidFieldType
+  |                  ^^^^ InvalidVariantType
   |
diff --git a/dhall/tests/type-inference/failure/unit/UnionTypeNotType.txt b/dhall/tests/type-inference/failure/unit/UnionTypeNotType.txt
index 450a3dd..cedf06e 100644
--- a/dhall/tests/type-inference/failure/unit/UnionTypeNotType.txt
+++ b/dhall/tests/type-inference/failure/unit/UnionTypeNotType.txt
@@ -1,6 +1,6 @@
-Type error: error: InvalidFieldType
- --> <current file>:1:1
+Type error: error: InvalidVariantType
+ --> <current file>:1:7
   |
 1 | < x : True >
-  | ^^^^^^^^^^^^ InvalidFieldType
+  |       ^^^^ InvalidVariantType
   |
diff --git a/tests_buffer b/tests_buffer
index afb270f..bd76d36 100644
--- a/tests_buffer
+++ b/tests_buffer
@@ -35,5 +35,6 @@ failure/
     merge { x = True, y = 1 } < x | y >.x
     merge {x=...,y=...} <x>.x
     merge {x=...,y=...} <x:T>.x
+fix unit_RightBiasedRecordMergeMixedKinds3 & 2 & unit_RecordMixedKinds3
 
 equivalence:
-- 
cgit v1.3.1