Merge pull request #104 from Nadrieril/rework-value

Rework Value

1 files changed, 295 insertions, 501 deletions

diff --git a/dhall/src/phase/typecheck.rs b/dhall/src/phase/typecheck.rs
index 56fb5ed..c47eb78 100644
--- a/dhall/src/phase/typecheck.rs
+++ b/dhall/src/phase/typecheck.rs
@@ -1,33 +1,29 @@
+use std::cmp::max;
 use std::collections::HashMap;
 
 use dhall_syntax::{
     rc, Builtin, Const, Expr, ExprF, InterpolatedTextContents, Label, SubExpr,
 };
 
-use crate::core::context::{NormalizationContext, TypecheckContext};
-use crate::core::thunk::{Thunk, TypedThunk};
+use crate::core::context::TypecheckContext;
 use crate::core::value::Value;
+use crate::core::valuef::ValueF;
 use crate::core::var::{Shift, Subst};
 use crate::error::{TypeError, TypeMessage};
-use crate::phase::{Normalized, Resolved, Type, Typed};
+use crate::phase::Normalized;
 
 fn tck_pi_type(
     ctx: &TypecheckContext,
     x: Label,
-    tx: Type,
-    te: Type,
-) -> Result<Typed, TypeError> {
+    tx: Value,
+    te: Value,
+) -> Result<Value, TypeError> {
     use crate::error::TypeMessage::*;
     let ctx2 = ctx.insert_type(&x, tx.clone());
 
     let ka = match tx.get_type()?.as_const() {
         Some(k) => k,
-        _ => {
-            return Err(TypeError::new(
-                ctx,
-                InvalidInputType(tx.to_normalized()),
-            ))
-        }
+        _ => return Err(TypeError::new(ctx, InvalidInputType(tx))),
     };
 
     let kb = match te.get_type()?.as_const() {
@@ -35,68 +31,58 @@ fn tck_pi_type(
         _ => {
             return Err(TypeError::new(
                 &ctx2,
-                InvalidOutputType(te.get_type()?.to_normalized()),
+                InvalidOutputType(te.get_type()?.into_owned()),
             ))
         }
     };
 
     let k = function_check(ka, kb);
 
-    Ok(Typed::from_thunk_and_type(
-        Value::Pi(
-            x.into(),
-            TypedThunk::from_type(tx),
-            TypedThunk::from_type(te),
-        )
-        .into_thunk(),
-        Type::from_const(k),
+    Ok(Value::from_valuef_and_type(
+        ValueF::Pi(x.into(), tx, te),
+        Value::from_const(k),
     ))
 }
 
 fn tck_record_type(
     ctx: &TypecheckContext,
-    kts: impl IntoIterator<Item = Result<(Label, Type), TypeError>>,
-) -> Result<Typed, TypeError> {
+    kts: impl IntoIterator<Item = Result<(Label, Value), TypeError>>,
+) -> Result<Value, TypeError> {
     use crate::error::TypeMessage::*;
     use std::collections::hash_map::Entry;
     let mut new_kts = HashMap::new();
-    // Check that all types are the same const
-    let mut k = None;
+    // An empty record type has type Type
+    let mut k = Const::Type;
     for e in kts {
         let (x, t) = e?;
-        match (k, t.get_type()?.as_const()) {
-            (None, Some(k2)) => k = Some(k2),
-            (Some(k1), Some(k2)) if k1 == k2 => {}
-            _ => {
-                return Err(TypeError::new(
-                    ctx,
-                    InvalidFieldType(x.clone(), t.clone()),
-                ))
-            }
+        // Construct the union of the contained `Const`s
+        match t.get_type()?.as_const() {
+            Some(k2) => k = max(k, k2),
+            None => return Err(TypeError::new(ctx, InvalidFieldType(x, t))),
         }
-        let entry = new_kts.entry(x.clone());
+        // Check for duplicated entries
+        let entry = new_kts.entry(x);
         match &entry {
             Entry::Occupied(_) => {
                 return Err(TypeError::new(ctx, RecordTypeDuplicateField))
             }
-            Entry::Vacant(_) => {
-                entry.or_insert_with(|| TypedThunk::from_type(t.clone()))
-            }
+            Entry::Vacant(_) => entry.or_insert_with(|| t),
         };
     }
-    // An empty record type has type Type
-    let k = k.unwrap_or(dhall_syntax::Const::Type);
 
-    Ok(Typed::from_thunk_and_type(
-        Value::RecordType(new_kts).into_thunk(),
-        Type::from_const(k),
+    Ok(Value::from_valuef_and_type(
+        ValueF::RecordType(new_kts),
+        Value::from_const(k),
     ))
 }
 
-fn tck_union_type(
+fn tck_union_type<Iter>(
     ctx: &TypecheckContext,
-    kts: impl IntoIterator<Item = Result<(Label, Option<Type>), TypeError>>,
-) -> Result<Typed, TypeError> {
+    kts: Iter,
+) -> Result<Value, TypeError>
+where
+    Iter: IntoIterator<Item = Result<(Label, Option<Value>), TypeError>>,
+{
     use crate::error::TypeMessage::*;
     use std::collections::hash_map::Entry;
     let mut new_kts = HashMap::new();
@@ -111,46 +97,42 @@ fn tck_union_type(
                 _ => {
                     return Err(TypeError::new(
                         ctx,
-                        InvalidFieldType(x.clone(), t.clone()),
+                        InvalidFieldType(x, t.clone()),
                     ))
                 }
             }
         }
-        let entry = new_kts.entry(x.clone());
+        let entry = new_kts.entry(x);
         match &entry {
             Entry::Occupied(_) => {
                 return Err(TypeError::new(ctx, UnionTypeDuplicateField))
             }
-            Entry::Vacant(_) => entry.or_insert_with(|| {
-                t.as_ref().map(|t| TypedThunk::from_type(t.clone()))
-            }),
+            Entry::Vacant(_) => entry.or_insert_with(|| t),
         };
     }
 
     // An empty union type has type Type;
     // an union type with only unary variants also has type Type
-    let k = k.unwrap_or(dhall_syntax::Const::Type);
+    let k = k.unwrap_or(Const::Type);
 
-    Ok(Typed::from_thunk_and_type(
-        Value::UnionType(new_kts).into_thunk(),
-        Type::from_const(k),
+    Ok(Value::from_valuef_and_type(
+        ValueF::UnionType(new_kts),
+        Value::from_const(k),
     ))
 }
 
 fn function_check(a: Const, b: Const) -> Const {
-    use dhall_syntax::Const::Type;
-    use std::cmp::max;
-    if b == Type {
-        Type
+    if b == Const::Type {
+        Const::Type
     } else {
         max(a, b)
     }
 }
 
-pub(crate) fn type_of_const(c: Const) -> Result<Type, TypeError> {
+pub(crate) fn type_of_const(c: Const) -> Result<Value, TypeError> {
     match c {
-        Const::Type => Ok(Type::from_const(Const::Kind)),
-        Const::Kind => Ok(Type::from_const(Const::Sort)),
+        Const::Type => Ok(Value::from_const(Const::Kind)),
+        Const::Kind => Ok(Value::from_const(Const::Sort)),
         Const::Sort => {
             Err(TypeError::new(&TypecheckContext::new(), TypeMessage::Sort))
         }
@@ -298,25 +280,9 @@ fn type_of_builtin<E>(b: Builtin) -> Expr<E> {
     }
 }
 
-/// Takes an expression that is meant to contain a Type
-/// and turn it into a type, typechecking it along the way.
-pub(crate) fn mktype(
-    ctx: &TypecheckContext,
-    e: SubExpr<Normalized>,
-) -> Result<Type, TypeError> {
-    Ok(type_with(ctx, e)?.to_type())
-}
-
-pub(crate) fn builtin_to_type(b: Builtin) -> Result<Type, TypeError> {
-    mktype(&TypecheckContext::new(), SubExpr::from_builtin(b))
-}
-
-/// Intermediary return type
-enum Ret {
-    /// Returns the contained value as is
-    RetWhole(Typed),
-    /// Use the contained Type as the type of the input expression
-    RetTypeOnly(Type),
+// TODO: this can't fail in practise
+pub(crate) fn builtin_to_type(b: Builtin) -> Result<Value, TypeError> {
+    type_with(&TypecheckContext::new(), SubExpr::from_builtin(b))
 }
 
 /// Type-check an expression and return the expression alongside its type if type-checking
@@ -326,28 +292,23 @@ enum Ret {
 fn type_with(
     ctx: &TypecheckContext,
     e: SubExpr<Normalized>,
-) -> Result<Typed, TypeError> {
+) -> Result<Value, TypeError> {
     use dhall_syntax::ExprF::{Annot, Embed, Lam, Let, Pi, Var};
 
-    use Ret::*;
     Ok(match e.as_ref() {
         Lam(x, t, b) => {
-            let tx = mktype(ctx, t.clone())?;
+            let tx = type_with(ctx, t.clone())?;
             let ctx2 = ctx.insert_type(x, tx.clone());
             let b = type_with(&ctx2, b.clone())?;
-            let v = Value::Lam(
-                x.clone().into(),
-                TypedThunk::from_type(tx.clone()),
-                b.to_thunk(),
-            );
+            let v = ValueF::Lam(x.clone().into(), tx.clone(), b.clone());
             let tb = b.get_type()?.into_owned();
-            let t = tck_pi_type(ctx, x.clone(), tx, tb)?.to_type();
-            Typed::from_thunk_and_type(Thunk::from_value(v), t)
+            let t = tck_pi_type(ctx, x.clone(), tx, tb)?;
+            Value::from_valuef_and_type(v, t)
         }
         Pi(x, ta, tb) => {
-            let ta = mktype(ctx, ta.clone())?;
+            let ta = type_with(ctx, ta.clone())?;
             let ctx2 = ctx.insert_type(x, ta.clone());
-            let tb = mktype(&ctx2, tb.clone())?;
+            let tb = type_with(&ctx2, tb.clone())?;
             return tck_pi_type(ctx, x.clone(), ta, tb);
         }
         Let(x, t, v, e) => {
@@ -360,9 +321,9 @@ fn type_with(
             let v = type_with(ctx, v)?;
             return type_with(&ctx.insert_value(x, v.clone())?, e.clone());
         }
-        Embed(p) => p.clone().into_typed(),
+        Embed(p) => p.clone().into_typed().into_value(),
         Var(var) => match ctx.lookup(&var) {
-            Some(typed) => typed,
+            Some(typed) => typed.clone(),
             None => {
                 return Err(TypeError::new(
                     ctx,
@@ -370,24 +331,13 @@ fn type_with(
                 ))
             }
         },
-        _ => {
+        e => {
             // Typecheck recursively all subexpressions
-            let expr =
-                e.as_ref().traverse_ref_with_special_handling_of_binders(
-                    |e| type_with(ctx, e.clone()),
-                    |_, _| unreachable!(),
-                )?;
-            let ret = type_last_layer(ctx, &expr)?;
-            match ret {
-                RetTypeOnly(typ) => {
-                    let expr = expr.map_ref(|typed| typed.to_thunk());
-                    Typed::from_thunk_and_type(
-                        Thunk::from_partial_expr(expr),
-                        typ,
-                    )
-                }
-                RetWhole(tt) => tt,
-            }
+            let expr = e.traverse_ref_with_special_handling_of_binders(
+                |e| type_with(ctx, e.clone()),
+                |_, _| unreachable!(),
+            )?;
+            type_last_layer(ctx, expr)?
         }
     })
 }
@@ -396,17 +346,25 @@ fn type_with(
 /// layer.
 fn type_last_layer(
     ctx: &TypecheckContext,
-    e: &ExprF<Typed, Normalized>,
-) -> Result<Ret, TypeError> {
+    e: ExprF<Value, Normalized>,
+) -> Result<Value, TypeError> {
     use crate::error::TypeMessage::*;
     use dhall_syntax::BinOp::*;
     use dhall_syntax::Builtin::*;
     use dhall_syntax::Const::Type;
     use dhall_syntax::ExprF::*;
+    let mkerr = |msg: TypeMessage| Err(TypeError::new(ctx, msg));
+
+    /// Intermediary return type
+    enum Ret {
+        /// Returns the contained value as is
+        RetWhole(Value),
+        /// Returns the input expression `e` with the contained value as its type
+        RetTypeOnly(Value),
+    }
     use Ret::*;
-    let mkerr = |msg: TypeMessage| TypeError::new(ctx, msg);
 
-    match e {
+    let ret = match &e {
         Import(_) => unreachable!(
             "There should remain no imports in a resolved expression"
         ),
@@ -415,456 +373,296 @@ fn type_last_layer(
         }
         App(f, a) => {
             let tf = f.get_type()?;
-            let (x, tx, tb) = match &tf.to_value() {
-                Value::Pi(x, tx, tb) => (x.clone(), tx.to_type(), tb.to_type()),
-                _ => return Err(mkerr(NotAFunction(f.clone()))),
+            let tf_borrow = tf.as_whnf();
+            let (x, tx, tb) = match &*tf_borrow {
+                ValueF::Pi(x, tx, tb) => (x, tx, tb),
+                _ => return mkerr(NotAFunction(f.clone())),
             };
-            if a.get_type()?.as_ref() != &tx {
-                return Err(mkerr(TypeMismatch(
-                    f.clone(),
-                    tx.to_normalized(),
-                    a.clone(),
-                )));
+            if a.get_type()?.as_ref() != tx {
+                return mkerr(TypeMismatch(f.clone(), tx.clone(), a.clone()));
             }
 
-            Ok(RetTypeOnly(tb.subst_shift(&x.into(), &a)))
+            RetTypeOnly(tb.subst_shift(&x.into(), a))
         }
         Annot(x, t) => {
-            let t = t.to_type();
-            if &t != x.get_type()?.as_ref() {
-                return Err(mkerr(AnnotMismatch(x.clone(), t.to_normalized())));
+            if t != x.get_type()?.as_ref() {
+                return mkerr(AnnotMismatch(x.clone(), t.clone()));
             }
-            Ok(RetTypeOnly(x.get_type()?.into_owned()))
+            RetTypeOnly(x.get_type()?.into_owned())
         }
         Assert(t) => {
-            match t.to_value() {
-                Value::Equivalence(ref x, ref y) if x == y => {}
-                Value::Equivalence(x, y) => {
-                    return Err(mkerr(AssertMismatch(
-                        x.to_typed(),
-                        y.to_typed(),
-                    )))
+            match &*t.as_whnf() {
+                ValueF::Equivalence(x, y) if x == y => {}
+                ValueF::Equivalence(x, y) => {
+                    return mkerr(AssertMismatch(x.clone(), y.clone()))
                 }
-                _ => return Err(mkerr(AssertMustTakeEquivalence)),
+                _ => return mkerr(AssertMustTakeEquivalence),
             }
-            Ok(RetTypeOnly(t.to_type()))
+            RetTypeOnly(t.clone())
         }
         BoolIf(x, y, z) => {
             if x.get_type()?.as_ref() != &builtin_to_type(Bool)? {
-                return Err(mkerr(InvalidPredicate(x.clone())));
+                return mkerr(InvalidPredicate(x.clone()));
             }
 
             if y.get_type()?.get_type()?.as_const() != Some(Type) {
-                return Err(mkerr(IfBranchMustBeTerm(true, y.clone())));
+                return mkerr(IfBranchMustBeTerm(true, y.clone()));
             }
 
             if z.get_type()?.get_type()?.as_const() != Some(Type) {
-                return Err(mkerr(IfBranchMustBeTerm(false, z.clone())));
+                return mkerr(IfBranchMustBeTerm(false, z.clone()));
             }
 
             if y.get_type()? != z.get_type()? {
-                return Err(mkerr(IfBranchMismatch(y.clone(), z.clone())));
+                return mkerr(IfBranchMismatch(y.clone(), z.clone()));
             }
 
-            Ok(RetTypeOnly(y.get_type()?.into_owned()))
+            RetTypeOnly(y.get_type()?.into_owned())
         }
         EmptyListLit(t) => {
-            let t = t.to_type();
-            match &t.to_value() {
-                Value::AppliedBuiltin(dhall_syntax::Builtin::List, args)
+            match &*t.as_whnf() {
+                ValueF::AppliedBuiltin(dhall_syntax::Builtin::List, args)
                     if args.len() == 1 => {}
-                _ => {
-                    return Err(TypeError::new(
-                        ctx,
-                        InvalidListType(t.to_normalized()),
-                    ))
-                }
+                _ => return mkerr(InvalidListType(t.clone())),
             }
-            Ok(RetTypeOnly(t))
+            RetTypeOnly(t.clone())
         }
         NEListLit(xs) => {
             let mut iter = xs.iter().enumerate();
             let (_, x) = iter.next().unwrap();
             for (i, y) in iter {
                 if x.get_type()? != y.get_type()? {
-                    return Err(mkerr(InvalidListElement(
+                    return mkerr(InvalidListElement(
                         i,
-                        x.get_type()?.to_normalized(),
+                        x.get_type()?.into_owned(),
                         y.clone(),
-                    )));
+                    ));
                 }
             }
             let t = x.get_type()?;
             if t.get_type()?.as_const() != Some(Type) {
-                return Err(TypeError::new(
-                    ctx,
-                    InvalidListType(t.to_normalized()),
-                ));
+                return mkerr(InvalidListType(t.into_owned()));
             }
 
-            Ok(RetTypeOnly(
-                Typed::from_thunk_and_type(
-                    Value::from_builtin(dhall_syntax::Builtin::List)
-                        .app(t.to_value())
-                        .into_thunk(),
-                    Typed::from_const(Type),
-                )
-                .to_type(),
+            RetTypeOnly(Value::from_valuef_and_type(
+                ValueF::from_builtin(dhall_syntax::Builtin::List)
+                    .app_value(t.into_owned()),
+                Value::from_const(Type),
             ))
         }
         SomeLit(x) => {
             let t = x.get_type()?.into_owned();
             if t.get_type()?.as_const() != Some(Type) {
-                return Err(TypeError::new(
-                    ctx,
-                    InvalidOptionalType(t.to_normalized()),
-                ));
+                return mkerr(InvalidOptionalType(t));
             }
 
-            Ok(RetTypeOnly(
-                Typed::from_thunk_and_type(
-                    Value::from_builtin(dhall_syntax::Builtin::Optional)
-                        .app(t.to_value())
-                        .into_thunk(),
-                    Typed::from_const(Type).into_type(),
-                )
-                .to_type(),
+            RetTypeOnly(Value::from_valuef_and_type(
+                ValueF::from_builtin(dhall_syntax::Builtin::Optional)
+                    .app_value(t),
+                Value::from_const(Type),
             ))
         }
-        RecordType(kts) => Ok(RetWhole(tck_record_type(
+        RecordType(kts) => RetWhole(tck_record_type(
             ctx,
-            kts.iter().map(|(x, t)| Ok((x.clone(), t.to_type()))),
-        )?)),
-        UnionType(kts) => Ok(RetWhole(tck_union_type(
+            kts.iter().map(|(x, t)| Ok((x.clone(), t.clone()))),
+        )?),
+        UnionType(kts) => RetWhole(tck_union_type(
             ctx,
-            kts.iter()
-                .map(|(x, t)| Ok((x.clone(), t.as_ref().map(|t| t.to_type())))),
-        )?)),
-        RecordLit(kvs) => Ok(RetTypeOnly(
-            tck_record_type(
-                ctx,
-                kvs.iter()
-                    .map(|(x, v)| Ok((x.clone(), v.get_type()?.into_owned()))),
-            )?
-            .into_type(),
-        )),
+            kts.iter().map(|(x, t)| Ok((x.clone(), t.clone()))),
+        )?),
+        RecordLit(kvs) => RetTypeOnly(tck_record_type(
+            ctx,
+            kvs.iter()
+                .map(|(x, v)| Ok((x.clone(), v.get_type()?.into_owned()))),
+        )?),
         Field(r, x) => {
-            match &r.get_type()?.to_value() {
-                Value::RecordType(kts) => match kts.get(&x) {
+            match &*r.get_type()?.as_whnf() {
+                ValueF::RecordType(kts) => match kts.get(&x) {
                     Some(tth) => {
-                        Ok(RetTypeOnly(tth.to_type()))
+                        RetTypeOnly(tth.clone())
                     },
-                    None => Err(mkerr(MissingRecordField(x.clone(),
-                                        r.clone()))),
+                    None => return mkerr(MissingRecordField(x.clone(),
+                                        r.clone())),
                 },
                 // TODO: branch here only when r.get_type() is a Const
                 _ => {
-                    let r = r.to_type();
-                    match &r.to_value() {
-                        Value::UnionType(kts) => match kts.get(&x) {
+                    match &*r.as_whnf() {
+                        ValueF::UnionType(kts) => match kts.get(&x) {
                             // Constructor has type T -> < x: T, ... >
                             Some(Some(t)) => {
-                                // TODO: avoid capture
-                                Ok(RetTypeOnly(
+                                RetTypeOnly(
                                     tck_pi_type(
                                         ctx,
                                         "_".into(),
-                                        t.to_type(),
-                                        r.clone(),
-                                    )?.to_type()
-                                ))
+                                        t.clone(),
+                                        r.under_binder(Label::from("_")),
+                                    )?
+                                )
                             },
                             Some(None) => {
-                                Ok(RetTypeOnly(r.clone()))
+                                RetTypeOnly(r.clone())
                             },
                             None => {
-                                Err(mkerr(MissingUnionField(
+                                return mkerr(MissingUnionField(
                                     x.clone(),
-                                    r.to_normalized(),
-                                )))
+                                    r.clone(),
+                                ))
                             },
                         },
                         _ => {
-                            Err(mkerr(NotARecord(
+                            return mkerr(NotARecord(
                                 x.clone(),
-                                r.to_normalized()
-                            )))
+                                r.clone()
+                            ))
                         },
                     }
                 }
-                // _ => Err(mkerr(NotARecord(
+                // _ => mkerr(NotARecord(
                 //     x,
-                //     r.to_type()?.to_normalized(),
-                // ))),
+                //     r?,
+                // )),
             }
         }
-        Const(c) => Ok(RetWhole(Typed::from_const(*c))),
-        Builtin(b) => Ok(RetTypeOnly(mktype(ctx, rc(type_of_builtin(*b)))?)),
-        BoolLit(_) => Ok(RetTypeOnly(builtin_to_type(Bool)?)),
-        NaturalLit(_) => Ok(RetTypeOnly(builtin_to_type(Natural)?)),
-        IntegerLit(_) => Ok(RetTypeOnly(builtin_to_type(Integer)?)),
-        DoubleLit(_) => Ok(RetTypeOnly(builtin_to_type(Double)?)),
+        Const(c) => RetWhole(Value::from_const(*c)),
+        Builtin(b) => RetTypeOnly(type_with(ctx, rc(type_of_builtin(*b)))?),
+        BoolLit(_) => RetTypeOnly(builtin_to_type(Bool)?),
+        NaturalLit(_) => RetTypeOnly(builtin_to_type(Natural)?),
+        IntegerLit(_) => RetTypeOnly(builtin_to_type(Integer)?),
+        DoubleLit(_) => RetTypeOnly(builtin_to_type(Double)?),
         TextLit(interpolated) => {
             let text_type = builtin_to_type(Text)?;
             for contents in interpolated.iter() {
                 use InterpolatedTextContents::Expr;
                 if let Expr(x) = contents {
                     if x.get_type()?.as_ref() != &text_type {
-                        return Err(mkerr(InvalidTextInterpolation(x.clone())));
+                        return mkerr(InvalidTextInterpolation(x.clone()));
                     }
                 }
             }
-            Ok(RetTypeOnly(text_type))
+            RetTypeOnly(text_type)
         }
         BinOp(RightBiasedRecordMerge, l, r) => {
             use crate::phase::normalize::merge_maps;
 
             let l_type = l.get_type()?;
-            let l_kind = l_type.get_type()?;
             let r_type = r.get_type()?;
-            let r_kind = r_type.get_type()?;
-
-            // Check the equality of kinds.
-            // This is to disallow expression such as:
-            // "{ x = Text } // { y = 1 }"
-            if l_kind != r_kind {
-                return Err(mkerr(RecordMismatch(l.clone(), r.clone())));
-            }
 
             // Extract the LHS record type
-            let kts_x = match l_type.to_value() {
-                Value::RecordType(kts) => kts,
-                _ => return Err(mkerr(MustCombineRecord(l.clone()))),
+            let l_type_borrow = l_type.as_whnf();
+            let kts_x = match &*l_type_borrow {
+                ValueF::RecordType(kts) => kts,
+                _ => return mkerr(MustCombineRecord(l.clone())),
             };
 
             // Extract the RHS record type
-            let kts_y = match r_type.to_value() {
-                Value::RecordType(kts) => kts,
-                _ => return Err(mkerr(MustCombineRecord(r.clone()))),
+            let r_type_borrow = r_type.as_whnf();
+            let kts_y = match &*r_type_borrow {
+                ValueF::RecordType(kts) => kts,
+                _ => return mkerr(MustCombineRecord(r.clone())),
             };
 
             // 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 kts = merge_maps(kts_x, kts_y, |_, r_t| r_t.clone());
 
             // Construct the final record type from the union
-            Ok(RetTypeOnly(
-                tck_record_type(
-                    ctx,
-                    kts.iter().map(|(x, v)| Ok((x.clone(), v.to_type()))),
-                )?
-                .into_type(),
-            ))
-        }
-        BinOp(RecursiveRecordMerge, l, r) => {
-            // A recursive function to dig down into
-            // records of records when merging.
-            fn combine_record_types(
-                ctx: &TypecheckContext,
-                kts_l: HashMap<Label, TypedThunk>,
-                kts_r: HashMap<Label, TypedThunk>,
-            ) -> Result<Typed, TypeError> {
-                use crate::phase::normalize::outer_join;
-
-                // If the Label exists for both records and Type for the values
-                // are records themselves, then we hit the recursive case.
-                // Otherwise we have a field collision.
-                let combine = |k: &Label,
-                               inner_l: &TypedThunk,
-                               inner_r: &TypedThunk|
-                 -> Result<Typed, TypeError> {
-                    match (inner_l.to_value(), inner_r.to_value()) {
-                        (
-                            Value::RecordType(inner_l_kvs),
-                            Value::RecordType(inner_r_kvs),
-                        ) => {
-                            combine_record_types(ctx, inner_l_kvs, inner_r_kvs)
-                        }
-                        (_, _) => {
-                            Err(TypeError::new(ctx, FieldCollision(k.clone())))
-                        }
-                    }
-                };
-
-                let kts: HashMap<Label, Result<Typed, TypeError>> = outer_join(
-                    |l| Ok(l.to_type()),
-                    |r| Ok(r.to_type()),
-                    |k: &Label, l: &TypedThunk, r: &TypedThunk| {
-                        combine(k, l, r)
-                    },
-                    &kts_l,
-                    &kts_r,
-                );
-
-                Ok(tck_record_type(
-                    ctx,
-                    kts.into_iter().map(|(x, v)| v.map(|r| (x.clone(), r))),
-                )?
-                .into_type())
-            };
-
-            let l_type = l.get_type()?;
-            let l_kind = l_type.get_type()?;
-            let r_type = r.get_type()?;
-            let r_kind = r_type.get_type()?;
-
-            // Check the equality of kinds.
-            // This is to disallow expression such as:
-            // "{ x = Text } // { y = 1 }"
-            if l_kind != r_kind {
-                return Err(mkerr(RecordMismatch(l.clone(), r.clone())));
-            }
-
-            // Extract the LHS record type
-            let kts_x = match l_type.to_value() {
-                Value::RecordType(kts) => kts,
-                _ => return Err(mkerr(MustCombineRecord(l.clone()))),
-            };
-
-            // Extract the RHS record type
-            let kts_y = match r_type.to_value() {
-                Value::RecordType(kts) => kts,
-                _ => return Err(mkerr(MustCombineRecord(r.clone()))),
-            };
-
-            combine_record_types(ctx, kts_x, kts_y).map(|r| RetTypeOnly(r))
+            RetTypeOnly(tck_record_type(
+                ctx,
+                kts.into_iter().map(|(x, v)| Ok((x.clone(), v))),
+            )?)
         }
+        BinOp(RecursiveRecordMerge, l, r) => RetTypeOnly(type_last_layer(
+            ctx,
+            ExprF::BinOp(
+                RecursiveRecordTypeMerge,
+                l.get_type()?.into_owned(),
+                r.get_type()?.into_owned(),
+            ),
+        )?),
         BinOp(RecursiveRecordTypeMerge, l, r) => {
-            // A recursive function to dig down into
-            // records of records when merging.
-            fn combine_record_types(
-                ctx: &TypecheckContext,
-                kts_l: HashMap<Label, TypedThunk>,
-                kts_r: HashMap<Label, TypedThunk>,
-            ) -> Result<Typed, TypeError> {
-                use crate::phase::normalize::intersection_with_key;
-
-                // If the Label exists for both records and Type for the values
-                // are records themselves, then we hit the recursive case.
-                // Otherwise we have a field collision.
-                let combine = |k: &Label,
-                               kts_l_inner: &TypedThunk,
-                               kts_r_inner: &TypedThunk|
-                 -> Result<Typed, TypeError> {
-                    match (kts_l_inner.to_value(), kts_r_inner.to_value()) {
-                        (
-                            Value::RecordType(kvs_l_inner),
-                            Value::RecordType(kvs_r_inner),
-                        ) => {
-                            combine_record_types(ctx, kvs_l_inner, kvs_r_inner)
-                        }
-                        (_, _) => {
-                            Err(TypeError::new(ctx, FieldCollision(k.clone())))
-                        }
-                    }
-                };
-
-                let kts = intersection_with_key(
-                    |k: &Label, l: &TypedThunk, r: &TypedThunk| {
-                        combine(k, l, r)
-                    },
-                    &kts_l,
-                    &kts_r,
-                );
-
-                Ok(tck_record_type(
-                    ctx,
-                    kts.into_iter().map(|(x, v)| v.map(|r| (x.clone(), r))),
-                )?
-                .into_type())
-            };
+            use crate::phase::normalize::intersection_with_key;
 
             // Extract the Const of the LHS
-            let k_l = match l.get_type()?.to_value() {
-                Value::Const(k) => k,
+            let k_l = match l.get_type()?.as_const() {
+                Some(k) => k,
                 _ => {
-                    return Err(mkerr(RecordTypeMergeRequiresRecordType(
-                        l.clone(),
-                    )))
+                    return mkerr(RecordTypeMergeRequiresRecordType(l.clone()))
                 }
             };
 
             // Extract the Const of the RHS
-            let k_r = match r.get_type()?.to_value() {
-                Value::Const(k) => k,
+            let k_r = match r.get_type()?.as_const() {
+                Some(k) => k,
                 _ => {
-                    return Err(mkerr(RecordTypeMergeRequiresRecordType(
-                        r.clone(),
-                    )))
+                    return mkerr(RecordTypeMergeRequiresRecordType(r.clone()))
                 }
             };
 
-            // Const values must match for the Records
-            let k = if k_l == k_r {
-                k_l
-            } else {
-                return Err(mkerr(RecordTypeMismatch(
-                    Typed::from_const(k_l),
-                    Typed::from_const(k_r),
-                    l.clone(),
-                    r.clone(),
-                )));
-            };
+            let k = max(k_l, k_r);
 
             // Extract the LHS record type
-            let kts_x = match l.to_value() {
-                Value::RecordType(kts) => kts,
+            let borrow_l = l.as_whnf();
+            let kts_x = match &*borrow_l {
+                ValueF::RecordType(kts) => kts,
                 _ => {
-                    return Err(mkerr(RecordTypeMergeRequiresRecordType(
-                        l.clone(),
-                    )))
+                    return mkerr(RecordTypeMergeRequiresRecordType(l.clone()))
                 }
             };
 
             // Extract the RHS record type
-            let kts_y = match r.to_value() {
-                Value::RecordType(kts) => kts,
+            let borrow_r = r.as_whnf();
+            let kts_y = match &*borrow_r {
+                ValueF::RecordType(kts) => kts,
                 _ => {
-                    return Err(mkerr(RecordTypeMergeRequiresRecordType(
-                        r.clone(),
-                    )))
+                    return mkerr(RecordTypeMergeRequiresRecordType(r.clone()))
                 }
             };
 
             // Ensure that the records combine without a type error
-            // and if not output the final Const value.
-            combine_record_types(ctx, kts_x, kts_y)
-                .and(Ok(RetTypeOnly(Typed::from_const(k))))
+            let kts = intersection_with_key(
+                // If the Label exists for both records, then we hit the recursive case.
+                |_: &Label, l: &Value, r: &Value| {
+                    type_last_layer(
+                        ctx,
+                        ExprF::BinOp(
+                            RecursiveRecordTypeMerge,
+                            l.clone(),
+                            r.clone(),
+                        ),
+                    )
+                },
+                kts_x,
+                kts_y,
+            );
+            tck_record_type(ctx, kts.into_iter().map(|(x, v)| Ok((x, v?))))?;
+
+            RetTypeOnly(Value::from_const(k))
         }
         BinOp(o @ ListAppend, l, r) => {
-            match l.get_type()?.to_value() {
-                Value::AppliedBuiltin(List, _) => {}
-                _ => return Err(mkerr(BinOpTypeMismatch(*o, l.clone()))),
+            match &*l.get_type()?.as_whnf() {
+                ValueF::AppliedBuiltin(List, _) => {}
+                _ => return mkerr(BinOpTypeMismatch(*o, l.clone())),
             }
 
             if l.get_type()? != r.get_type()? {
-                return Err(mkerr(BinOpTypeMismatch(*o, r.clone())));
+                return mkerr(BinOpTypeMismatch(*o, r.clone()));
             }
 
-            Ok(RetTypeOnly(l.get_type()?.into_owned()))
+            RetTypeOnly(l.get_type()?.into_owned())
         }
         BinOp(Equivalence, l, r) => {
             if l.get_type()?.get_type()?.as_const() != Some(Type) {
-                return Err(mkerr(EquivalenceArgumentMustBeTerm(
-                    true,
-                    l.clone(),
-                )));
+                return mkerr(EquivalenceArgumentMustBeTerm(true, l.clone()));
             }
             if r.get_type()?.get_type()?.as_const() != Some(Type) {
-                return Err(mkerr(EquivalenceArgumentMustBeTerm(
-                    false,
-                    r.clone(),
-                )));
+                return mkerr(EquivalenceArgumentMustBeTerm(false, r.clone()));
             }
 
             if l.get_type()? != r.get_type()? {
-                return Err(mkerr(EquivalenceTypeMismatch(
-                    r.clone(),
-                    l.clone(),
-                )));
+                return mkerr(EquivalenceTypeMismatch(r.clone(), l.clone()));
             }
 
-            Ok(RetTypeOnly(Typed::from_const(Type).into_type()))
+            RetTypeOnly(Value::from_const(Type))
         }
         BinOp(o, l, r) => {
             let t = builtin_to_type(match o {
@@ -884,140 +682,136 @@ fn type_last_layer(
             })?;
 
             if l.get_type()?.as_ref() != &t {
-                return Err(mkerr(BinOpTypeMismatch(*o, l.clone())));
+                return mkerr(BinOpTypeMismatch(*o, l.clone()));
             }
 
             if r.get_type()?.as_ref() != &t {
-                return Err(mkerr(BinOpTypeMismatch(*o, r.clone())));
+                return mkerr(BinOpTypeMismatch(*o, r.clone()));
             }
 
-            Ok(RetTypeOnly(t))
+            RetTypeOnly(t)
         }
         Merge(record, union, type_annot) => {
-            let handlers = match record.get_type()?.to_value() {
-                Value::RecordType(kts) => kts,
-                _ => return Err(mkerr(Merge1ArgMustBeRecord(record.clone()))),
+            let record_type = record.get_type()?;
+            let record_borrow = record_type.as_whnf();
+            let handlers = match &*record_borrow {
+                ValueF::RecordType(kts) => kts,
+                _ => return mkerr(Merge1ArgMustBeRecord(record.clone())),
             };
 
-            let variants = match union.get_type()?.to_value() {
-                Value::UnionType(kts) => kts,
-                _ => return Err(mkerr(Merge2ArgMustBeUnion(union.clone()))),
+            let union_type = union.get_type()?;
+            let union_borrow = union_type.as_whnf();
+            let variants = match &*union_borrow {
+                ValueF::UnionType(kts) => kts,
+                _ => return mkerr(Merge2ArgMustBeUnion(union.clone())),
             };
 
             let mut inferred_type = None;
-            for (x, handler) in handlers.iter() {
-                let handler_return_type = match variants.get(x) {
-                    // Union alternative with type
-                    Some(Some(variant_type)) => {
-                        let variant_type = variant_type.to_type();
-                        let handler_type = handler.to_type();
-                        let (x, tx, tb) = match &handler_type.to_value() {
-                            Value::Pi(x, tx, tb) => {
-                                (x.clone(), tx.to_type(), tb.to_type())
+            for (x, handler_type) in handlers {
+                let handler_return_type =
+                    match variants.get(x) {
+                        // Union alternative with type
+                        Some(Some(variant_type)) => {
+                            let handler_type_borrow = handler_type.as_whnf();
+                            let (x, tx, tb) = match &*handler_type_borrow {
+                                ValueF::Pi(x, tx, tb) => (x, tx, tb),
+                                _ => {
+                                    return mkerr(NotAFunction(
+                                        handler_type.clone(),
+                                    ))
+                                }
+                            };
+
+                            if variant_type != tx {
+                                return mkerr(TypeMismatch(
+                                    handler_type.clone(),
+                                    tx.clone(),
+                                    variant_type.clone(),
+                                ));
                             }
-                            _ => return Err(mkerr(NotAFunction(handler_type))),
-                        };
-
-                        if &variant_type != &tx {
-                            return Err(mkerr(TypeMismatch(
-                                handler_type,
-                                tx.to_normalized(),
-                                variant_type,
-                            )));
-                        }
 
-                        // Extract `tb` from under the `x` binder. Fails is `x` was free in `tb`.
-                        match tb.over_binder(x) {
-                            Some(x) => x,
-                            None => {
-                                return Err(mkerr(
+                            // Extract `tb` from under the `x` binder. Fails is `x` was free in `tb`.
+                            match tb.over_binder(x) {
+                                Some(x) => x,
+                                None => return mkerr(
                                     MergeHandlerReturnTypeMustNotBeDependent,
-                                ))
+                                ),
                             }
                         }
-                    }
-                    // Union alternative without type
-                    Some(None) => handler.to_type(),
-                    None => {
-                        return Err(mkerr(MergeHandlerMissingVariant(
-                            x.clone(),
-                        )))
-                    }
-                };
+                        // Union alternative without type
+                        Some(None) => handler_type.clone(),
+                        None => {
+                            return mkerr(MergeHandlerMissingVariant(x.clone()))
+                        }
+                    };
                 match &inferred_type {
                     None => inferred_type = Some(handler_return_type),
                     Some(t) => {
                         if t != &handler_return_type {
-                            return Err(mkerr(MergeHandlerTypeMismatch));
+                            return mkerr(MergeHandlerTypeMismatch);
                         }
                     }
                 }
             }
             for x in variants.keys() {
                 if !handlers.contains_key(x) {
-                    return Err(mkerr(MergeVariantMissingHandler(x.clone())));
+                    return mkerr(MergeVariantMissingHandler(x.clone()));
                 }
             }
 
             match (inferred_type, type_annot) {
                 (Some(ref t1), Some(t2)) => {
-                    let t2 = t2.to_type();
-                    if t1 != &t2 {
-                        return Err(mkerr(MergeAnnotMismatch));
+                    if t1 != t2 {
+                        return mkerr(MergeAnnotMismatch);
                     }
-                    Ok(RetTypeOnly(t2))
+                    RetTypeOnly(t2.clone())
                 }
-                (Some(t), None) => Ok(RetTypeOnly(t)),
-                (None, Some(t)) => Ok(RetTypeOnly(t.to_type())),
-                (None, None) => Err(mkerr(MergeEmptyNeedsAnnotation)),
+                (Some(t), None) => RetTypeOnly(t),
+                (None, Some(t)) => RetTypeOnly(t.clone()),
+                (None, None) => return mkerr(MergeEmptyNeedsAnnotation),
             }
         }
         Projection(record, labels) => {
-            let trecord = record.get_type()?;
-            let kts = match trecord.to_value() {
-                Value::RecordType(kts) => kts,
-                _ => return Err(mkerr(ProjectionMustBeRecord)),
+            let record_type = record.get_type()?;
+            let record_borrow = record_type.as_whnf();
+            let kts = match &*record_borrow {
+                ValueF::RecordType(kts) => kts,
+                _ => return mkerr(ProjectionMustBeRecord),
             };
 
             let mut new_kts = HashMap::new();
             for l in labels {
                 match kts.get(l) {
-                    None => return Err(mkerr(ProjectionMissingEntry)),
+                    None => return mkerr(ProjectionMissingEntry),
                     Some(t) => new_kts.insert(l.clone(), t.clone()),
                 };
             }
 
-            Ok(RetTypeOnly(
-                Typed::from_thunk_and_type(
-                    Value::RecordType(new_kts).into_thunk(),
-                    trecord.get_type()?.into_owned(),
-                )
-                .to_type(),
+            RetTypeOnly(Value::from_valuef_and_type(
+                ValueF::RecordType(new_kts),
+                record_type.get_type()?.into_owned(),
             ))
         }
-    }
+    };
+
+    Ok(match ret {
+        RetTypeOnly(typ) => {
+            Value::from_valuef_and_type(ValueF::PartialExpr(e), typ)
+        }
+        RetWhole(v) => v,
+    })
 }
 
-/// `typeOf` is the same as `type_with` with an empty context, meaning that the
+/// `type_of` is the same as `type_with` with an empty context, meaning that the
 /// expression must be closed (i.e. no free variables), otherwise type-checking
 /// will fail.
-fn type_of(e: SubExpr<Normalized>) -> Result<Typed, TypeError> {
-    let ctx = TypecheckContext::new();
-    let e = type_with(&ctx, e)?;
-    // Ensure `e` has a type (i.e. `e` is not `Sort`)
-    e.get_type()?;
-    Ok(e)
+pub(crate) fn typecheck(e: SubExpr<Normalized>) -> Result<Value, TypeError> {
+    type_with(&TypecheckContext::new(), e)
 }
 
-pub(crate) fn typecheck(e: Resolved) -> Result<Typed, TypeError> {
-    type_of(e.0)
-}
-
-pub(crate) fn typecheck_with(e: Resolved, ty: &Type) -> Result<Typed, TypeError> {
-    let expr: SubExpr<_> = e.0;
-    let ty: SubExpr<_> = ty.to_expr();
-    type_of(expr.rewrap(ExprF::Annot(expr.clone(), ty)))
-}
-pub(crate) fn skip_typecheck(e: Resolved) -> Typed {
-    Typed::from_thunk_untyped(Thunk::new(NormalizationContext::new(), e.0))
+pub(crate) fn typecheck_with(
+    expr: SubExpr<Normalized>,
+    ty: SubExpr<Normalized>,
+) -> Result<Value, TypeError> {
+    typecheck(expr.rewrap(ExprF::Annot(expr.clone(), ty)))
 }