From 7374d0524ccd53b256107667b213597c05720d2d Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Sun, 31 Mar 2019 19:08:08 +0200
Subject: Move recursion out of Expr

---
 dhall/src/binary.rs               |   4 +-
 dhall/src/normalize.rs            |   6 +-
 dhall/src/typecheck.rs            |   6 +-
 dhall/tests/common/mod.rs         |   2 +-
 dhall_core/src/core.rs            |  76 +++++++----------
 dhall_core/src/parser.rs          | 172 +++++++++++++++++++-------------------
 dhall_core/src/printer.rs         |   8 +-
 dhall_core/src/text.rs            |  37 ++++----
 dhall_generator/src/dhall_expr.rs |  36 ++++----
 dhall_generator/src/dhall_type.rs |   4 +-
 10 files changed, 170 insertions(+), 181 deletions(-)

diff --git a/dhall/src/binary.rs b/dhall/src/binary.rs
index 988891b..1ba1873 100644
--- a/dhall/src/binary.rs
+++ b/dhall/src/binary.rs
@@ -20,10 +20,10 @@ pub fn decode(data: &[u8]) -> Result<ParsedExpr, DecodeError> {
 fn cbor_value_to_dhall(data: &cbor::Value) -> Result<ParsedExpr, DecodeError> {
     use cbor::Value::*;
     use dhall_core::{BinOp, Builtin, Const};
-    use Expr::*;
+    use ExprF::*;
     Ok(rc(match data {
         String(s) => match Builtin::parse(s) {
-            Some(b) => Expr::Builtin(b),
+            Some(b) => ExprF::Builtin(b),
             None => match s.as_str() {
                 "True" => BoolLit(true),
                 "False" => BoolLit(false),
diff --git a/dhall/src/normalize.rs b/dhall/src/normalize.rs
index 5405e88..c6c294c 100644
--- a/dhall/src/normalize.rs
+++ b/dhall/src/normalize.rs
@@ -12,7 +12,7 @@ where
     A: fmt::Debug,
 {
     use dhall_core::Builtin::*;
-    use dhall_core::Expr::*;
+    use dhall_core::ExprF::*;
     let f = rc(Builtin(b));
     // How many arguments a builtin needs, and which argument
     // should be normalized and pattern-matched
@@ -199,7 +199,7 @@ where
     // Put the remaining arguments back and eval again. In most cases
     // ret will not be of a form that can be applied, so this won't go very deep.
     // In lots of cases, there are no remaining args so this cann will just return ret.
-    normalize_whnf(&rc(Expr::App(ret, args.split_off(len_consumption))))
+    normalize_whnf(&rc(ExprF::App(ret, args.split_off(len_consumption))))
 }
 
 /// Reduce an expression to its weak head normal form, i.e. normalize
@@ -213,7 +213,7 @@ where
     A: fmt::Debug,
 {
     use dhall_core::BinOp::*;
-    use dhall_core::Expr::*;
+    use dhall_core::ExprF::*;
     match e.as_ref() {
         Let(f, _, r, b) => {
             let vf0 = &V(f.clone(), 0);
diff --git a/dhall/src/typecheck.rs b/dhall/src/typecheck.rs
index e769c7f..31702db 100644
--- a/dhall/src/typecheck.rs
+++ b/dhall/src/typecheck.rs
@@ -12,7 +12,7 @@ use self::TypeMessage::*;
 
 fn axiom<S>(c: Const) -> Result<Const, TypeError<S>> {
     use dhall_core::Const::*;
-    use dhall_core::Expr::*;
+    use dhall_core::ExprF::*;
     match c {
         Type => Ok(Kind),
         Kind => Err(TypeError::new(&Context::new(), rc(Const(Kind)), Untyped)),
@@ -53,7 +53,7 @@ where
     S: ::std::fmt::Debug,
     T: ::std::fmt::Debug,
 {
-    use dhall_core::Expr::*;
+    use dhall_core::ExprF::*;
     fn go<S, T>(
         ctx: &mut Vec<(Label, Label)>,
         el: &Expr<S, X>,
@@ -192,7 +192,7 @@ where
     use dhall_core::BinOp::*;
     use dhall_core::Builtin::*;
     use dhall_core::Const::*;
-    use dhall_core::Expr::*;
+    use dhall_core::ExprF::*;
     let mkerr = |msg: TypeMessage<_>| TypeError::new(ctx, e.clone(), msg);
     let ensure_const = |x: &SubExpr<_, _>, msg: TypeMessage<_>| match x.as_ref()
     {
diff --git a/dhall/tests/common/mod.rs b/dhall/tests/common/mod.rs
index 6b893e0..325b80f 100644
--- a/dhall/tests/common/mod.rs
+++ b/dhall/tests/common/mod.rs
@@ -111,7 +111,7 @@ pub fn run_test(base_path: &str, feature: Feature) {
             let expected_file_path = base_path + "B.dhall";
             let expr = rc(read_dhall_file(&expr_file_path).unwrap());
             let expected = rc(read_dhall_file(&expected_file_path).unwrap());
-            typecheck::type_of(rc(Expr::Annot(expr, expected))).unwrap();
+            typecheck::type_of(rc(ExprF::Annot(expr, expected))).unwrap();
         }
     }
 }
diff --git a/dhall_core/src/core.rs b/dhall_core/src/core.rs
index b49515a..2d11068 100644
--- a/dhall_core/src/core.rs
+++ b/dhall_core/src/core.rs
@@ -173,43 +173,39 @@ pub type DhallExpr = ResolvedExpr;
 #[derive(Debug, PartialEq, Eq)]
 pub struct SubExpr<Note, Embed>(pub Rc<Expr<Note, Embed>>);
 
+pub type Expr<Note, Embed> = ExprF<SubExpr<Note, Embed>, Note, Embed>;
+
 /// Syntax tree for expressions
+// Having the recursion out of the enum definition enables writing
+// much more generic code and improves pattern-matching behind
+// smart pointers.
 #[derive(Debug, Clone, PartialEq, Eq)]
-pub enum Expr<Note, Embed> {
+pub enum ExprF<SubExpr, Note, Embed> {
     ///  `Const c                                  ~  c`
     Const(Const),
     ///  `Var (V x 0)                              ~  x`<br>
     ///  `Var (V x n)                              ~  x@n`
     Var(V),
     ///  `Lam x     A b                            ~  λ(x : A) -> b`
-    Lam(Label, SubExpr<Note, Embed>, SubExpr<Note, Embed>),
+    Lam(Label, SubExpr, SubExpr),
     ///  `Pi "_" A B                               ~        A  -> B`
     ///  `Pi x   A B                               ~  ∀(x : A) -> B`
-    Pi(Label, SubExpr<Note, Embed>, SubExpr<Note, Embed>),
+    Pi(Label, SubExpr, SubExpr),
     ///  `App f A                                  ~  f A`
-    App(SubExpr<Note, Embed>, Vec<SubExpr<Note, Embed>>),
+    App(SubExpr, Vec<SubExpr>),
     ///  `Let x Nothing  r e  ~  let x     = r in e`
     ///  `Let x (Just t) r e  ~  let x : t = r in e`
-    Let(
-        Label,
-        Option<SubExpr<Note, Embed>>,
-        SubExpr<Note, Embed>,
-        SubExpr<Note, Embed>,
-    ),
+    Let(Label, Option<SubExpr>, SubExpr, SubExpr),
     ///  `Annot x t                                ~  x : t`
-    Annot(SubExpr<Note, Embed>, SubExpr<Note, Embed>),
+    Annot(SubExpr, SubExpr),
     /// Built-in values
     Builtin(Builtin),
     // Binary operations
-    BinOp(BinOp, SubExpr<Note, Embed>, SubExpr<Note, Embed>),
+    BinOp(BinOp, SubExpr, SubExpr),
     ///  `BoolLit b                                ~  b`
     BoolLit(bool),
     ///  `BoolIf x y z                             ~  if x then y else z`
-    BoolIf(
-        SubExpr<Note, Embed>,
-        SubExpr<Note, Embed>,
-        SubExpr<Note, Embed>,
-    ),
+    BoolIf(SubExpr, SubExpr, SubExpr),
     ///  `NaturalLit n                             ~  +n`
     NaturalLit(Natural),
     ///  `IntegerLit n                             ~  n`
@@ -217,39 +213,31 @@ pub enum Expr<Note, Embed> {
     ///  `DoubleLit n                              ~  n`
     DoubleLit(Double),
     ///  `TextLit t                                ~  t`
-    TextLit(InterpolatedText<Note, Embed>),
+    TextLit(InterpolatedText<SubExpr>),
     ///  [] : List t`
-    EmptyListLit(SubExpr<Note, Embed>),
+    EmptyListLit(SubExpr),
     ///  [x, y, z]
-    NEListLit(Vec<SubExpr<Note, Embed>>),
+    NEListLit(Vec<SubExpr>),
     ///  None t
-    EmptyOptionalLit(SubExpr<Note, Embed>),
+    EmptyOptionalLit(SubExpr),
     ///  Some e
-    NEOptionalLit(SubExpr<Note, Embed>),
+    NEOptionalLit(SubExpr),
     ///  `Record            [(k1, t1), (k2, t2)]   ~  { k1 : t1, k2 : t1 }`
-    RecordType(BTreeMap<Label, SubExpr<Note, Embed>>),
+    RecordType(BTreeMap<Label, SubExpr>),
     ///  `RecordLit         [(k1, v1), (k2, v2)]   ~  { k1 = v1, k2 = v2 }`
-    RecordLit(BTreeMap<Label, SubExpr<Note, Embed>>),
+    RecordLit(BTreeMap<Label, SubExpr>),
     ///  `Union             [(k1, t1), (k2, t2)]   ~  < k1 : t1, k2 : t2 >`
-    UnionType(BTreeMap<Label, SubExpr<Note, Embed>>),
+    UnionType(BTreeMap<Label, SubExpr>),
     ///  `UnionLit (k1, v1) [(k2, t2), (k3, t3)]   ~  < k1 = t1, k2 : t2, k3 : t3 >`
-    UnionLit(
-        Label,
-        SubExpr<Note, Embed>,
-        BTreeMap<Label, SubExpr<Note, Embed>>,
-    ),
+    UnionLit(Label, SubExpr, BTreeMap<Label, SubExpr>),
     ///  `Merge x y t                              ~  merge x y : t`
-    Merge(
-        SubExpr<Note, Embed>,
-        SubExpr<Note, Embed>,
-        Option<SubExpr<Note, Embed>>,
-    ),
+    Merge(SubExpr, SubExpr, Option<SubExpr>),
     ///  e.x
-    Field(SubExpr<Note, Embed>, Label),
+    Field(SubExpr, Label),
     ///  e.{ x, y, z }
-    Projection(SubExpr<Note, Embed>, Vec<Label>),
+    Projection(SubExpr, Vec<Label>),
     /// Annotation on the AST. Unused for now but could hold e.g. file location information
-    Note(Note, SubExpr<Note, Embed>),
+    Note(Note, SubExpr),
     /// Embeds an import or the result of resolving the import
     Embed(Embed),
 }
@@ -305,7 +293,7 @@ impl<S, A> Expr<S, A> {
 impl<S: Clone, A: Clone> Expr<S, Expr<S, A>> {
     pub fn squash_embed(&self) -> Expr<S, A> {
         match self {
-            Expr::Embed(e) => e.clone(),
+            ExprF::Embed(e) => e.clone(),
             e => e.map_shallow(
                 |e| e.squash_embed(),
                 |x| x.clone(),
@@ -369,7 +357,7 @@ where
     F4: Fn(&Label) -> Label,
     F5: FnOnce(&Label, &SubExpr<S, A>) -> SubExpr<T, B>,
 {
-    use crate::Expr::*;
+    use crate::ExprF::*;
     let map = &map;
     let opt = |x: &Option<_>| x.as_ref().map(&map);
     let vec = |x: &Vec<_>| x.iter().map(&map).collect();
@@ -422,8 +410,8 @@ where
     F2: FnOnce(&Label, &SubExpr<S, A>) -> SubExpr<S, A>,
 {
     match e.as_ref() {
-        Expr::Embed(_) => SubExpr::clone(e),
-        Expr::Note(_, e) => {
+        ExprF::Embed(_) => SubExpr::clone(e),
+        ExprF::Note(_, e) => {
             map_subexpr_rc_binder(e, map_expr, map_under_binder)
         }
         _ => rc(map_subexpr(
@@ -523,7 +511,7 @@ pub fn shift<S, A>(
     var: &V,
     in_expr: &SubExpr<S, A>,
 ) -> SubExpr<S, A> {
-    use crate::Expr::*;
+    use crate::ExprF::*;
     let V(x, n) = var;
     let under_binder = |y: &Label, e: &SubExpr<_, _>| {
         let n = if x == y { n + 1 } else { *n };
@@ -553,7 +541,7 @@ pub fn subst<S, A>(
     value: &SubExpr<S, A>,
     in_expr: &SubExpr<S, A>,
 ) -> SubExpr<S, A> {
-    use crate::Expr::*;
+    use crate::ExprF::*;
     let under_binder = |y: &Label, e: &SubExpr<_, _>| {
         let V(x, n) = var;
         let n = if x == y { n + 1 } else { *n };
diff --git a/dhall_core/src/parser.rs b/dhall_core/src/parser.rs
index b7ac3f6..343a895 100644
--- a/dhall_core/src/parser.rs
+++ b/dhall_core/src/parser.rs
@@ -13,8 +13,10 @@ use crate::*;
 // their own crate because they are quite general and useful. For now they
 // are here and hopefully you can figure out how they work.
 
-type ParsedText = InterpolatedText<X, Import>;
-type ParsedTextContents = InterpolatedTextContents<X, Import>;
+use crate::ExprF::*;
+
+type ParsedText = InterpolatedText<SubExpr<X, Import>>;
+type ParsedTextContents = InterpolatedTextContents<SubExpr<X, Import>>;
 
 pub type ParseError = pest::error::Error<Rule>;
 
@@ -26,9 +28,9 @@ enum Either<A, B> {
     Right(B),
 }
 
-impl Builtin {
+impl crate::Builtin {
     pub fn parse(s: &str) -> Option<Self> {
-        use self::Builtin::*;
+        use crate::Builtin::*;
         match s {
             "Bool" => Some(Bool),
             "Natural" => Some(Natural),
@@ -267,7 +269,7 @@ make_parser! {
     ));
     rule!(unreserved_label<Label>; children!(
         [label(l)] => {
-            if Builtin::parse(&String::from(&l)).is_some() {
+            if crate::Builtin::parse(&String::from(&l)).is_some() {
                 Err(
                     format!("Builtin names are not allowed as bound variables")
                 )?
@@ -526,13 +528,13 @@ make_parser! {
 
     rule!(import<ParsedExpr> as expression; children!(
         [import_hashed(location_hashed)] => {
-            bx(Expr::Embed(Import {
+            bx(Embed(Import {
                 mode: ImportMode::Code,
                 location_hashed
             }))
         },
         [import_hashed(location_hashed), Text(_)] => {
-            bx(Expr::Embed(Import {
+            bx(Embed(Import {
                 mode: ImportMode::RawText,
                 location_hashed
             }))
@@ -541,13 +543,13 @@ make_parser! {
 
     rule!(lambda_expression<ParsedExpr> as expression; children!(
         [unreserved_label(l), expression(typ), expression(body)] => {
-            bx(Expr::Lam(l, typ, body))
+            bx(Lam(l, typ, body))
         }
     ));
 
     rule!(ifthenelse_expression<ParsedExpr> as expression; children!(
         [expression(cond), expression(left), expression(right)] => {
-            bx(Expr::BoolIf(cond, left, right))
+            bx(BoolIf(cond, left, right))
         }
     ));
 
@@ -555,7 +557,7 @@ make_parser! {
         [let_binding(bindings).., expression(final_expr)] => {
             bindings.fold(
                 final_expr,
-                |acc, x| bx(Expr::Let(x.0, x.1, x.2, acc))
+                |acc, x| bx(Let(x.0, x.1, x.2, acc))
             )
         }
     ));
@@ -569,21 +571,21 @@ make_parser! {
 
     rule!(forall_expression<ParsedExpr> as expression; children!(
         [unreserved_label(l), expression(typ), expression(body)] => {
-            bx(Expr::Pi(l, typ, body))
+            bx(Pi(l, typ, body))
         }
     ));
 
     rule!(arrow_expression<ParsedExpr> as expression; children!(
         [expression(typ), expression(body)] => {
-            bx(Expr::Pi("_".into(), typ, body))
+            bx(Pi("_".into(), typ, body))
         }
     ));
 
     rule!(merge_expression<ParsedExpr> as expression; children!(
         [expression(x), expression(y), expression(z)] =>
-            bx(Expr::Merge(x, y, Some(z))),
+            bx(Merge(x, y, Some(z))),
         [expression(x), expression(y)] =>
-            bx(Expr::Merge(x, y, None)),
+            bx(Merge(x, y, None)),
     ));
 
     rule!(List<()>; captured_str!(_) => ());
@@ -591,108 +593,108 @@ make_parser! {
 
     rule!(empty_collection<ParsedExpr> as expression; children!(
         [List(_), expression(t)] => {
-            bx(Expr::EmptyListLit(t))
+            bx(EmptyListLit(t))
         },
         [Optional(_), expression(t)] => {
-            bx(Expr::EmptyOptionalLit(t))
+            bx(EmptyOptionalLit(t))
         },
     ));
 
     rule!(non_empty_optional<ParsedExpr> as expression; children!(
         [expression(x), Optional(_), expression(t)] => {
-            rc(Expr::Annot(rc(Expr::NEOptionalLit(x)), t))
+            rc(Annot(rc(NEOptionalLit(x)), t))
         }
     ));
 
     rule!(import_alt_expression<ParsedExpr> as expression; children!(
         [expression(e)] => e,
         [expression(first), expression(rest)..] => {
-            let o = BinOp::ImportAlt;
-            rest.fold(first, |acc, e| bx(Expr::BinOp(o, acc, e)))
+            let o = crate::BinOp::ImportAlt;
+            rest.fold(first, |acc, e| bx(BinOp(o, acc, e)))
         },
     ));
     rule!(or_expression<ParsedExpr> as expression; children!(
         [expression(e)] => e,
         [expression(first), expression(rest)..] => {
-            let o = BinOp::BoolOr;
-            rest.fold(first, |acc, e| bx(Expr::BinOp(o, acc, e)))
+            let o = crate::BinOp::BoolOr;
+            rest.fold(first, |acc, e| bx(BinOp(o, acc, e)))
         },
     ));
     rule!(plus_expression<ParsedExpr> as expression; children!(
         [expression(e)] => e,
         [expression(first), expression(rest)..] => {
-            let o = BinOp::NaturalPlus;
-            rest.fold(first, |acc, e| bx(Expr::BinOp(o, acc, e)))
+            let o = crate::BinOp::NaturalPlus;
+            rest.fold(first, |acc, e| bx(BinOp(o, acc, e)))
         },
     ));
     rule!(text_append_expression<ParsedExpr> as expression; children!(
         [expression(e)] => e,
         [expression(first), expression(rest)..] => {
-            let o = BinOp::TextAppend;
-            rest.fold(first, |acc, e| bx(Expr::BinOp(o, acc, e)))
+            let o = crate::BinOp::TextAppend;
+            rest.fold(first, |acc, e| bx(BinOp(o, acc, e)))
         },
     ));
     rule!(list_append_expression<ParsedExpr> as expression; children!(
         [expression(e)] => e,
         [expression(first), expression(rest)..] => {
-            let o = BinOp::ListAppend;
-            rest.fold(first, |acc, e| bx(Expr::BinOp(o, acc, e)))
+            let o = crate::BinOp::ListAppend;
+            rest.fold(first, |acc, e| bx(BinOp(o, acc, e)))
         },
     ));
     rule!(and_expression<ParsedExpr> as expression; children!(
         [expression(e)] => e,
         [expression(first), expression(rest)..] => {
-            let o = BinOp::BoolAnd;
-            rest.fold(first, |acc, e| bx(Expr::BinOp(o, acc, e)))
+            let o = crate::BinOp::BoolAnd;
+            rest.fold(first, |acc, e| bx(BinOp(o, acc, e)))
         },
     ));
     rule!(combine_expression<ParsedExpr> as expression; children!(
         [expression(e)] => e,
         [expression(first), expression(rest)..] => {
-            let o = BinOp::Combine;
-            rest.fold(first, |acc, e| bx(Expr::BinOp(o, acc, e)))
+            let o = crate::BinOp::Combine;
+            rest.fold(first, |acc, e| bx(BinOp(o, acc, e)))
         },
     ));
     rule!(prefer_expression<ParsedExpr> as expression; children!(
         [expression(e)] => e,
         [expression(first), expression(rest)..] => {
-            let o = BinOp::Prefer;
-            rest.fold(first, |acc, e| bx(Expr::BinOp(o, acc, e)))
+            let o = crate::BinOp::Prefer;
+            rest.fold(first, |acc, e| bx(BinOp(o, acc, e)))
         },
     ));
     rule!(combine_types_expression<ParsedExpr> as expression; children!(
         [expression(e)] => e,
         [expression(first), expression(rest)..] => {
-            let o = BinOp::CombineTypes;
-            rest.fold(first, |acc, e| bx(Expr::BinOp(o, acc, e)))
+            let o = crate::BinOp::CombineTypes;
+            rest.fold(first, |acc, e| bx(BinOp(o, acc, e)))
         },
     ));
     rule!(times_expression<ParsedExpr> as expression; children!(
         [expression(e)] => e,
         [expression(first), expression(rest)..] => {
-            let o = BinOp::NaturalTimes;
-            rest.fold(first, |acc, e| bx(Expr::BinOp(o, acc, e)))
+            let o = crate::BinOp::NaturalTimes;
+            rest.fold(first, |acc, e| bx(BinOp(o, acc, e)))
         },
     ));
     rule!(equal_expression<ParsedExpr> as expression; children!(
         [expression(e)] => e,
         [expression(first), expression(rest)..] => {
-            let o = BinOp::BoolEQ;
-            rest.fold(first, |acc, e| bx(Expr::BinOp(o, acc, e)))
+            let o = crate::BinOp::BoolEQ;
+            rest.fold(first, |acc, e| bx(BinOp(o, acc, e)))
         },
     ));
     rule!(not_equal_expression<ParsedExpr> as expression; children!(
         [expression(e)] => e,
         [expression(first), expression(rest)..] => {
-            let o = BinOp::BoolNE;
-            rest.fold(first, |acc, e| bx(Expr::BinOp(o, acc, e)))
+            let o = crate::BinOp::BoolNE;
+            rest.fold(first, |acc, e| bx(BinOp(o, acc, e)))
         },
     ));
 
     rule!(annotated_expression<ParsedExpr> as expression; children!(
         [expression(e)] => e,
         [expression(e), expression(annot)] => {
-            bx(Expr::Annot(e, annot))
+            bx(Annot(e, annot))
         },
     ));
 
@@ -700,22 +702,22 @@ make_parser! {
         [expression(e)] => e,
         [expression(first), expression(second)] => {
             match first.as_ref() {
-                Expr::Builtin(Builtin::OptionalNone) =>
-                    bx(Expr::EmptyOptionalLit(second)),
-                Expr::Builtin(Builtin::OptionalSome) =>
-                    bx(Expr::NEOptionalLit(second)),
-                _ => bx(Expr::App(first, vec![second])),
+                Builtin(crate::Builtin::OptionalNone) =>
+                    bx(EmptyOptionalLit(second)),
+                Builtin(crate::Builtin::OptionalSome) =>
+                    bx(NEOptionalLit(second)),
+                _ => bx(App(first, vec![second])),
             }
         },
         [expression(first), expression(second), expression(rest)..] => {
             match first.as_ref() {
-                Expr::Builtin(Builtin::OptionalNone) =>
-                    bx(Expr::App(bx(Expr::EmptyOptionalLit(second)),
+                Builtin(crate::Builtin::OptionalNone) =>
+                    bx(App(bx(EmptyOptionalLit(second)),
                                  rest.collect())),
-                Expr::Builtin(Builtin::OptionalSome) =>
-                    bx(Expr::App(bx(Expr::NEOptionalLit(second)),
+                Builtin(crate::Builtin::OptionalSome) =>
+                    bx(App(bx(NEOptionalLit(second)),
                                  rest.collect())),
-                _ => bx(Expr::App(first,
+                _ => bx(App(first,
                                   std::iter::once(second)
                                     .chain(rest)
                                     .collect())),
@@ -727,8 +729,8 @@ make_parser! {
         [expression(e)] => e,
         [expression(first), selector(rest)..] => {
             rest.fold(first, |acc, e| match e {
-                Either::Left(l) => bx(Expr::Field(acc, l)),
-                Either::Right(ls) => bx(Expr::Projection(acc, ls)),
+                Either::Left(l) => bx(Field(acc, l)),
+                Either::Right(ls) => bx(Projection(acc, ls)),
             })
         }
     ));
@@ -743,66 +745,66 @@ make_parser! {
     ));
 
     rule!(literal_expression<ParsedExpr> as expression; children!(
-        [double_literal(n)] => bx(Expr::DoubleLit(n)),
+        [double_literal(n)] => bx(DoubleLit(n)),
         [minus_infinity_literal(n)] =>
-            bx(Expr::DoubleLit(std::f64::NEG_INFINITY.into())),
+            bx(DoubleLit(std::f64::NEG_INFINITY.into())),
         [plus_infinity_literal(n)] =>
-            bx(Expr::DoubleLit(std::f64::INFINITY.into())),
-        [NaN(n)] => bx(Expr::DoubleLit(std::f64::NAN.into())),
-        [natural_literal(n)] => bx(Expr::NaturalLit(n)),
-        [integer_literal(n)] => bx(Expr::IntegerLit(n)),
-        [double_quote_literal(s)] => bx(Expr::TextLit(s)),
-        [single_quote_literal(s)] => bx(Expr::TextLit(s)),
+            bx(DoubleLit(std::f64::INFINITY.into())),
+        [NaN(n)] => bx(DoubleLit(std::f64::NAN.into())),
+        [natural_literal(n)] => bx(NaturalLit(n)),
+        [integer_literal(n)] => bx(IntegerLit(n)),
+        [double_quote_literal(s)] => bx(TextLit(s)),
+        [single_quote_literal(s)] => bx(TextLit(s)),
         [expression(e)] => e,
     ));
 
     rule!(identifier<ParsedExpr> as expression; children!(
         [label(l), natural_literal(idx)] => {
             let name = String::from(&l);
-            match Builtin::parse(name.as_str()) {
-                Some(b) => bx(Expr::Builtin(b)),
+            match crate::Builtin::parse(name.as_str()) {
+                Some(b) => bx(Builtin(b)),
                 None => match name.as_str() {
-                    "True" => bx(Expr::BoolLit(true)),
-                    "False" => bx(Expr::BoolLit(false)),
-                    "Type" => bx(Expr::Const(Const::Type)),
-                    "Kind" => bx(Expr::Const(Const::Kind)),
-                    _ => bx(Expr::Var(V(l, idx))),
+                    "True" => bx(BoolLit(true)),
+                    "False" => bx(BoolLit(false)),
+                    "Type" => bx(Const(crate::Const::Type)),
+                    "Kind" => bx(Const(crate::Const::Kind)),
+                    _ => bx(Var(V(l, idx))),
                 }
             }
         },
         [label(l)] => {
             let name = String::from(&l);
-            match Builtin::parse(name.as_str()) {
-                Some(b) => bx(Expr::Builtin(b)),
+            match crate::Builtin::parse(name.as_str()) {
+                Some(b) => bx(Builtin(b)),
                 None => match name.as_str() {
-                    "True" => bx(Expr::BoolLit(true)),
-                    "False" => bx(Expr::BoolLit(false)),
-                    "Type" => bx(Expr::Const(Const::Type)),
-                    "Kind" => bx(Expr::Const(Const::Kind)),
-                    _ => bx(Expr::Var(V(l, 0))),
+                    "True" => bx(BoolLit(true)),
+                    "False" => bx(BoolLit(false)),
+                    "Type" => bx(Const(crate::Const::Type)),
+                    "Kind" => bx(Const(crate::Const::Kind)),
+                    _ => bx(Var(V(l, 0))),
                 }
             }
         },
     ));
 
     rule!(empty_record_literal<ParsedExpr> as expression;
-        captured_str!(_) => bx(Expr::RecordLit(BTreeMap::new()))
+        captured_str!(_) => bx(RecordLit(BTreeMap::new()))
     );
 
     rule!(empty_record_type<ParsedExpr> as expression;
-        captured_str!(_) => bx(Expr::RecordType(BTreeMap::new()))
+        captured_str!(_) => bx(RecordType(BTreeMap::new()))
     );
 
     rule!(non_empty_record_type_or_literal<ParsedExpr> as expression; children!(
         [label(first_label), non_empty_record_type(rest)] => {
             let (first_expr, mut map) = rest;
             map.insert(first_label, first_expr);
-            bx(Expr::RecordType(map))
+            bx(RecordType(map))
         },
         [label(first_label), non_empty_record_literal(rest)] => {
             let (first_expr, mut map) = rest;
             map.insert(first_label, first_expr);
-            bx(Expr::RecordLit(map))
+            bx(RecordLit(map))
         },
     ));
 
@@ -830,13 +832,13 @@ make_parser! {
 
     rule!(union_type_or_literal<ParsedExpr> as expression; children!(
         [empty_union_type(_)] => {
-            bx(Expr::UnionType(BTreeMap::new()))
+            bx(UnionType(BTreeMap::new()))
         },
         [non_empty_union_type_or_literal((Some((l, e)), entries))] => {
-            bx(Expr::UnionLit(l, e, entries))
+            bx(UnionLit(l, e, entries))
         },
         [non_empty_union_type_or_literal((None, entries))] => {
-            bx(Expr::UnionType(entries))
+            bx(UnionType(entries))
         },
     ));
 
@@ -869,7 +871,7 @@ make_parser! {
     ));
 
     rule!(non_empty_list_literal<ParsedExpr> as expression; children!(
-        [expression(items)..] => bx(Expr::NEListLit(items.collect()))
+        [expression(items)..] => bx(NEListLit(items.collect()))
     ));
 
     rule!(final_expression<ParsedExpr> as expression; children!(
@@ -885,7 +887,7 @@ pub fn parse_expr(s: &str) -> ParseResult<ParsedExpr> {
         ParsedValue::expression(e) => Ok(e),
         _ => unreachable!(),
     }
-    // Ok(bx(Expr::BoolLit(false)))
+    // Ok(bx(BoolLit(false)))
 }
 
 #[test]
diff --git a/dhall_core/src/printer.rs b/dhall_core/src/printer.rs
index b153d1b..b7d7506 100644
--- a/dhall_core/src/printer.rs
+++ b/dhall_core/src/printer.rs
@@ -35,7 +35,7 @@ impl<S, A: Display> Expr<S, A> {
         f: &mut fmt::Formatter,
         phase: PrintPhase,
     ) -> Result<(), fmt::Error> {
-        use crate::Expr::*;
+        use crate::ExprF::*;
         use PrintPhase::*;
         match self {
             _ if phase == Paren => {
@@ -143,7 +143,7 @@ impl<S, A: Display> Expr<S, A> {
                 write!(f, " : ")?;
                 b.fmt(f)?;
             }
-            Expr::BinOp(op, a, b) => {
+            ExprF::BinOp(op, a, b) => {
                 // Precedence is magically handled by the ordering of BinOps.
                 if phase > PrintPhase::BinOp(*op) {
                     return self.fmt_phase(f, Paren);
@@ -152,7 +152,7 @@ impl<S, A: Display> Expr<S, A> {
                 write!(f, " {} ", op)?;
                 b.fmt_phase(f, PrintPhase::BinOp(*op))?;
             }
-            Expr::App(a, args) => {
+            ExprF::App(a, args) => {
                 if phase > PrintPhase::App {
                     return self.fmt_phase(f, Paren);
                 }
@@ -239,7 +239,7 @@ where
     f.write_str(close)
 }
 
-impl<S, A: Display> Display for InterpolatedText<S, A> {
+impl<SubExpr: Display + Clone> Display for InterpolatedText<SubExpr> {
     fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
         f.write_str("\"")?;
         for x in self.iter() {
diff --git a/dhall_core/src/text.rs b/dhall_core/src/text.rs
index eef0797..d915553 100644
--- a/dhall_core/src/text.rs
+++ b/dhall_core/src/text.rs
@@ -1,17 +1,16 @@
-use crate::*;
 use std::iter::FromIterator;
 use std::ops::Add;
 
 #[derive(Debug, Clone, PartialEq, Eq)]
-pub struct InterpolatedText<Note, Embed> {
+pub struct InterpolatedText<SubExpr> {
     head: String,
-    tail: Vec<(SubExpr<Note, Embed>, String)>,
+    tail: Vec<(SubExpr, String)>,
 }
 
-impl<N, E> From<(String, Vec<(SubExpr<N, E>, String)>)>
-    for InterpolatedText<N, E>
+impl<SubExpr> From<(String, Vec<(SubExpr, String)>)>
+    for InterpolatedText<SubExpr>
 {
-    fn from(x: (String, Vec<(SubExpr<N, E>, String)>)) -> Self {
+    fn from(x: (String, Vec<(SubExpr, String)>)) -> Self {
         InterpolatedText {
             head: x.0,
             tail: x.1,
@@ -19,7 +18,7 @@ impl<N, E> From<(String, Vec<(SubExpr<N, E>, String)>)>
     }
 }
 
-impl<N, E> From<String> for InterpolatedText<N, E> {
+impl<SubExpr> From<String> for InterpolatedText<SubExpr> {
     fn from(s: String) -> Self {
         InterpolatedText {
             head: s,
@@ -29,15 +28,15 @@ impl<N, E> From<String> for InterpolatedText<N, E> {
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
-pub enum InterpolatedTextContents<Note, Embed> {
+pub enum InterpolatedTextContents<SubExpr> {
     Text(String),
-    Expr(SubExpr<Note, Embed>),
+    Expr(SubExpr),
 }
 
-impl<N, E> InterpolatedText<N, E> {
-    pub fn map<N2, E2, F>(&self, mut f: F) -> InterpolatedText<N2, E2>
+impl<SubExpr: Clone> InterpolatedText<SubExpr> {
+    pub fn map<SubExpr2, F>(&self, mut f: F) -> InterpolatedText<SubExpr2>
     where
-        F: FnMut(&SubExpr<N, E>) -> SubExpr<N2, E2>,
+        F: FnMut(&SubExpr) -> SubExpr2,
     {
         InterpolatedText {
             head: self.head.clone(),
@@ -47,7 +46,7 @@ impl<N, E> InterpolatedText<N, E> {
 
     pub fn iter<'a>(
         &'a self,
-    ) -> impl Iterator<Item = InterpolatedTextContents<N, E>> + 'a {
+    ) -> impl Iterator<Item = InterpolatedTextContents<SubExpr>> + 'a {
         use std::iter::once;
         once(InterpolatedTextContents::Text(self.head.clone())).chain(
             self.tail.iter().flat_map(|(e, s)| {
@@ -58,12 +57,12 @@ impl<N, E> InterpolatedText<N, E> {
     }
 }
 
-impl<'a, N: 'a, E: 'a> FromIterator<InterpolatedTextContents<N, E>>
-    for InterpolatedText<N, E>
+impl<'a, SubExpr: Clone + 'a> FromIterator<InterpolatedTextContents<SubExpr>>
+    for InterpolatedText<SubExpr>
 {
     fn from_iter<T>(iter: T) -> Self
     where
-        T: IntoIterator<Item = InterpolatedTextContents<N, E>>,
+        T: IntoIterator<Item = InterpolatedTextContents<SubExpr>>,
     {
         let mut res = InterpolatedText {
             head: "".to_owned(),
@@ -83,9 +82,9 @@ impl<'a, N: 'a, E: 'a> FromIterator<InterpolatedTextContents<N, E>>
     }
 }
 
-impl<N, E> Add for &InterpolatedText<N, E> {
-    type Output = InterpolatedText<N, E>;
-    fn add(self, rhs: &InterpolatedText<N, E>) -> Self::Output {
+impl<SubExpr: Clone> Add for &InterpolatedText<SubExpr> {
+    type Output = InterpolatedText<SubExpr>;
+    fn add(self, rhs: &InterpolatedText<SubExpr>) -> Self::Output {
         self.iter().chain(rhs.iter()).collect()
     }
 }
diff --git a/dhall_generator/src/dhall_expr.rs b/dhall_generator/src/dhall_expr.rs
index e2187d6..c4b15e8 100644
--- a/dhall_generator/src/dhall_expr.rs
+++ b/dhall_generator/src/dhall_expr.rs
@@ -21,7 +21,7 @@ fn dhall_to_tokenstream(
     expr: &DhallExpr,
     ctx: &Context<Label, ()>,
 ) -> TokenStream {
-    use dhall_core::Expr::*;
+    use dhall_core::ExprF::*;
     match expr.as_ref() {
         Var(_) => {
             let v = dhall_to_tokenstream_bx(expr, ctx);
@@ -31,66 +31,66 @@ fn dhall_to_tokenstream(
             let t = dhall_to_tokenstream_bx(t, ctx);
             let b = dhall_to_tokenstream_bx(b, &ctx.insert(x.clone(), ()));
             let x = label_to_tokenstream(x);
-            quote! { dhall_core::Expr::Pi(#x, #t, #b) }
+            quote! { dhall_core::ExprF::Pi(#x, #t, #b) }
         }
         Lam(x, t, b) => {
             let t = dhall_to_tokenstream_bx(t, ctx);
             let b = dhall_to_tokenstream_bx(b, &ctx.insert(x.clone(), ()));
             let x = label_to_tokenstream(x);
-            quote! { dhall_core::Expr::Lam(#x, #t, #b) }
+            quote! { dhall_core::ExprF::Lam(#x, #t, #b) }
         }
         App(f, a) => {
             let f = dhall_to_tokenstream_bx(f, ctx);
             let a = vec_to_tokenstream(a, ctx);
-            quote! { dhall_core::Expr::App(#f, #a) }
+            quote! { dhall_core::ExprF::App(#f, #a) }
         }
         Const(c) => {
             let c = const_to_tokenstream(*c);
-            quote! { dhall_core::Expr::Const(#c) }
+            quote! { dhall_core::ExprF::Const(#c) }
         }
         Builtin(b) => {
             let b = builtin_to_tokenstream(*b);
-            quote! { dhall_core::Expr::Builtin(#b) }
+            quote! { dhall_core::ExprF::Builtin(#b) }
         }
         BinOp(o, a, b) => {
             let o = binop_to_tokenstream(*o);
             let a = dhall_to_tokenstream_bx(a, ctx);
             let b = dhall_to_tokenstream_bx(b, ctx);
-            quote! { dhall_core::Expr::BinOp(#o, #a, #b) }
+            quote! { dhall_core::ExprF::BinOp(#o, #a, #b) }
         }
         NaturalLit(n) => {
-            quote! { dhall_core::Expr::NaturalLit(#n) }
+            quote! { dhall_core::ExprF::NaturalLit(#n) }
         }
         BoolLit(b) => {
-            quote! { dhall_core::Expr::BoolLit(#b) }
+            quote! { dhall_core::ExprF::BoolLit(#b) }
         }
         EmptyOptionalLit(x) => {
             let x = dhall_to_tokenstream_bx(x, ctx);
-            quote! { dhall_core::Expr::EmptyOptionalLit(#x) }
+            quote! { dhall_core::ExprF::EmptyOptionalLit(#x) }
         }
         NEOptionalLit(x) => {
             let x = dhall_to_tokenstream_bx(x, ctx);
-            quote! { dhall_core::Expr::NEOptionalLit(#x) }
+            quote! { dhall_core::ExprF::NEOptionalLit(#x) }
         }
         EmptyListLit(t) => {
             let t = dhall_to_tokenstream_bx(t, ctx);
-            quote! { dhall_core::Expr::EmptyListLit(#t) }
+            quote! { dhall_core::ExprF::EmptyListLit(#t) }
         }
         NEListLit(es) => {
             let es = vec_to_tokenstream(es, ctx);
-            quote! { dhall_core::Expr::NEListLit(#es) }
+            quote! { dhall_core::ExprF::NEListLit(#es) }
         }
         RecordType(m) => {
             let m = map_to_tokenstream(m, ctx);
-            quote! { dhall_core::Expr::RecordType(#m) }
+            quote! { dhall_core::ExprF::RecordType(#m) }
         }
         RecordLit(m) => {
             let m = map_to_tokenstream(m, ctx);
-            quote! { dhall_core::Expr::RecordLit(#m) }
+            quote! { dhall_core::ExprF::RecordLit(#m) }
         }
         UnionType(m) => {
             let m = map_to_tokenstream(m, ctx);
-            quote! { dhall_core::Expr::UnionType(#m) }
+            quote! { dhall_core::ExprF::UnionType(#m) }
         }
         e => unimplemented!("{:?}", e),
     }
@@ -101,7 +101,7 @@ fn dhall_to_tokenstream_bx(
     expr: &DhallExpr,
     ctx: &Context<Label, ()>,
 ) -> TokenStream {
-    use dhall_core::Expr::*;
+    use dhall_core::ExprF::*;
     match expr.as_ref() {
         Var(V(s, n)) => {
             match ctx.lookup(&s, *n) {
@@ -109,7 +109,7 @@ fn dhall_to_tokenstream_bx(
                 Some(()) => {
                     let s: String = s.into();
                     let var = quote! { dhall_core::V(#s.into(), #n) };
-                    bx(quote! { dhall_core::Expr::Var(#var) })
+                    bx(quote! { dhall_core::ExprF::Var(#var) })
                 }
                 // Free variable; interpolates as a rust variable
                 None => {
diff --git a/dhall_generator/src/dhall_type.rs b/dhall_generator/src/dhall_type.rs
index 270c27c..876d261 100644
--- a/dhall_generator/src/dhall_type.rs
+++ b/dhall_generator/src/dhall_type.rs
@@ -48,7 +48,7 @@ pub fn derive_for_struct(
             );
         }
     });
-    Ok(quote! { dhall_core::rc(dhall_core::Expr::RecordType({
+    Ok(quote! { dhall_core::rc(dhall_core::ExprF::RecordType({
         use std::collections::BTreeMap;
         let mut m = BTreeMap::new();
         #(#fields)*
@@ -101,7 +101,7 @@ pub fn derive_for_enum(
         })
         .collect::<Result<Vec<_>, Error>>()?;
 
-    Ok(quote! { dhall_core::rc(dhall_core::Expr::UnionType({
+    Ok(quote! { dhall_core::rc(dhall_core::ExprF::UnionType({
         use std::collections::BTreeMap;
         let mut m = BTreeMap::new();
         #(#variants)*
-- 
cgit v1.2.3