Move main datatypes into their own modules

4 files changed, 1050 insertions, 0 deletions

diff --git a/dhall/src/core/context.rs b/dhall/src/core/context.rs
new file mode 100644
index 0000000..9b5beed
--- /dev/null
+++ b/dhall/src/core/context.rs
@@ -0,0 +1,136 @@
+use std::borrow::Cow;
+use std::rc::Rc;
+
+use dhall_syntax::context::Context;
+use dhall_syntax::{Label, V};
+
+use crate::core::thunk::Thunk;
+use crate::core::value::{AlphaVar, Value};
+use crate::phase::{Normalized, Type, Typed};
+
+#[derive(Debug, Clone)]
+enum NzEnvItem {
+    Thunk(Thunk),
+    Skip(AlphaVar),
+}
+
+#[derive(Debug, Clone)]
+pub(crate) struct NormalizationContext(Rc<Context<Label, NzEnvItem>>);
+
+#[derive(Debug, Clone)]
+pub(crate) enum TyEnvItem {
+    Type(AlphaVar, Type),
+    Value(Normalized),
+}
+
+#[derive(Debug, Clone)]
+pub(crate) struct TypecheckContext(pub(crate) Context<Label, TyEnvItem>);
+
+impl NzEnvItem {
+    pub(crate) fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
+        use NzEnvItem::*;
+        match self {
+            Thunk(e) => Thunk(e.shift(delta, var)),
+            Skip(v) => Skip(v.shift(delta, var)),
+        }
+    }
+
+    pub(crate) fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self {
+        match self {
+            NzEnvItem::Thunk(e) => NzEnvItem::Thunk(e.subst_shift(var, val)),
+            NzEnvItem::Skip(v) if v == var => NzEnvItem::Thunk(val.to_thunk()),
+            NzEnvItem::Skip(v) => NzEnvItem::Skip(v.shift(-1, var)),
+        }
+    }
+}
+
+impl NormalizationContext {
+    pub(crate) fn new() -> Self {
+        NormalizationContext(Rc::new(Context::new()))
+    }
+    pub(crate) fn skip(&self, x: &Label) -> Self {
+        NormalizationContext(Rc::new(
+            self.0
+                .map(|_, e| e.shift(1, &x.into()))
+                .insert(x.clone(), NzEnvItem::Skip(x.into())),
+        ))
+    }
+    pub(crate) fn lookup(&self, var: &V<Label>) -> Value {
+        let V(x, n) = var;
+        match self.0.lookup(x, *n) {
+            Some(NzEnvItem::Thunk(t)) => t.to_value(),
+            Some(NzEnvItem::Skip(newvar)) => Value::Var(newvar.clone()),
+            // Free variable
+            None => Value::Var(AlphaVar::from_var(var.clone())),
+        }
+    }
+    pub(crate) fn from_typecheck_ctx(tc_ctx: &TypecheckContext) -> Self {
+        use TyEnvItem::*;
+        let mut ctx = Context::new();
+        for (k, vs) in tc_ctx.0.iter_keys() {
+            for v in vs.iter() {
+                let new_item = match v {
+                    Type(var, _) => NzEnvItem::Skip(var.clone()),
+                    Value(e) => NzEnvItem::Thunk(e.to_thunk()),
+                };
+                ctx = ctx.insert(k.clone(), new_item);
+            }
+        }
+        NormalizationContext(Rc::new(ctx))
+    }
+
+    pub(crate) fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
+        NormalizationContext(Rc::new(self.0.map(|_, e| e.shift(delta, var))))
+    }
+
+    pub(crate) fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self {
+        NormalizationContext(Rc::new(
+            self.0.map(|_, e| e.subst_shift(var, val)),
+        ))
+    }
+}
+
+impl TyEnvItem {
+    fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
+        use TyEnvItem::*;
+        match self {
+            Type(v, e) => Type(v.shift(delta, var), e.shift(delta, var)),
+            Value(e) => Value(e.shift(delta, var)),
+        }
+    }
+}
+
+impl TypecheckContext {
+    pub(crate) fn new() -> Self {
+        TypecheckContext(Context::new())
+    }
+    pub(crate) fn insert_type(&self, x: &Label, t: Type) -> Self {
+        TypecheckContext(self.0.map(|_, e| e.shift(1, &x.into())).insert(
+            x.clone(),
+            TyEnvItem::Type(x.into(), t.shift(1, &x.into())),
+        ))
+    }
+    pub(crate) fn insert_value(&self, x: &Label, t: Normalized) -> Self {
+        TypecheckContext(self.0.insert(x.clone(), TyEnvItem::Value(t)))
+    }
+    pub(crate) fn lookup(&self, var: &V<Label>) -> Option<Cow<'_, Type>> {
+        let V(x, n) = var;
+        match self.0.lookup(x, *n) {
+            Some(TyEnvItem::Type(_, t)) => Some(Cow::Borrowed(&t)),
+            Some(TyEnvItem::Value(t)) => Some(t.get_type()?),
+            None => None,
+        }
+    }
+    pub(crate) fn to_normalization_ctx(&self) -> NormalizationContext {
+        NormalizationContext::from_typecheck_ctx(self)
+    }
+}
+
+impl PartialEq for TypecheckContext {
+    fn eq(&self, _: &Self) -> bool {
+        // don't count contexts when comparing stuff
+        // this is dirty but needed for now
+        true
+    }
+}
+impl Eq for TypecheckContext {}
diff --git a/dhall/src/core/mod.rs b/dhall/src/core/mod.rs
new file mode 100644
index 0000000..8f5c2ca
--- /dev/null
+++ b/dhall/src/core/mod.rs
@@ -0,0 +1,3 @@
+pub(crate) mod context;
+pub(crate) mod thunk;
+pub(crate) mod value;
diff --git a/dhall/src/core/thunk.rs b/dhall/src/core/thunk.rs
new file mode 100644
index 0000000..8775ce2
--- /dev/null
+++ b/dhall/src/core/thunk.rs
@@ -0,0 +1,295 @@
+use std::cell::{Ref, RefCell};
+use std::rc::Rc;
+
+use crate::core::context::NormalizationContext;
+use crate::core::context::TypecheckContext;
+use crate::core::value::{AlphaVar, Value};
+use crate::error::TypeError;
+use crate::phase::normalize::{
+    apply_any, normalize_whnf, InputSubExpr, OutputSubExpr,
+};
+use crate::phase::typecheck::mktype;
+use crate::phase::{Type, Typed};
+
+#[derive(Debug, Clone, Copy)]
+enum Marker {
+    /// Weak Head Normal Form, i.e. subexpressions may not be normalized
+    WHNF,
+    /// Normal form, i.e. completely normalized
+    NF,
+}
+use Marker::{NF, WHNF};
+
+#[derive(Debug)]
+enum ThunkInternal {
+    /// Non-normalized value alongside a normalization context
+    Unnormalized(NormalizationContext, InputSubExpr),
+    /// Partially normalized value.
+    /// Invariant: if the marker is `NF`, the value must be fully normalized
+    Value(Marker, Value),
+}
+
+/// Stores a possibly unevaluated value. Uses RefCell to ensure that
+/// the value gets normalized at most once.
+#[derive(Debug, Clone)]
+pub struct Thunk(Rc<RefCell<ThunkInternal>>);
+
+/// A thunk in type position.
+#[derive(Debug, Clone)]
+pub(crate) enum TypeThunk {
+    Thunk(Thunk),
+    Type(Type),
+}
+
+impl ThunkInternal {
+    fn into_thunk(self) -> Thunk {
+        Thunk(Rc::new(RefCell::new(self)))
+    }
+
+    fn normalize_whnf(&mut self) {
+        match self {
+            ThunkInternal::Unnormalized(ctx, e) => {
+                *self = ThunkInternal::Value(
+                    WHNF,
+                    normalize_whnf(ctx.clone(), e.clone()),
+                )
+            }
+            // Already at least in WHNF
+            ThunkInternal::Value(_, _) => {}
+        }
+    }
+
+    fn normalize_nf(&mut self) {
+        match self {
+            ThunkInternal::Unnormalized(_, _) => {
+                self.normalize_whnf();
+                self.normalize_nf();
+            }
+            ThunkInternal::Value(m @ WHNF, v) => {
+                v.normalize_mut();
+                *m = NF;
+            }
+            // Already in NF
+            ThunkInternal::Value(NF, _) => {}
+        }
+    }
+
+    // Always use normalize_whnf before
+    fn as_whnf(&self) -> &Value {
+        match self {
+            ThunkInternal::Unnormalized(_, _) => unreachable!(),
+            ThunkInternal::Value(_, v) => v,
+        }
+    }
+
+    // Always use normalize_nf before
+    fn as_nf(&self) -> &Value {
+        match self {
+            ThunkInternal::Unnormalized(_, _) => unreachable!(),
+            ThunkInternal::Value(WHNF, _) => unreachable!(),
+            ThunkInternal::Value(NF, v) => v,
+        }
+    }
+
+    fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
+        match self {
+            ThunkInternal::Unnormalized(ctx, e) => {
+                ThunkInternal::Unnormalized(ctx.shift(delta, var), e.clone())
+            }
+            ThunkInternal::Value(m, v) => {
+                ThunkInternal::Value(*m, v.shift(delta, var))
+            }
+        }
+    }
+
+    fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self {
+        match self {
+            ThunkInternal::Unnormalized(ctx, e) => ThunkInternal::Unnormalized(
+                ctx.subst_shift(var, val),
+                e.clone(),
+            ),
+            ThunkInternal::Value(_, v) => {
+                // The resulting value may not stay in normal form after substitution
+                ThunkInternal::Value(WHNF, v.subst_shift(var, val))
+            }
+        }
+    }
+}
+
+impl Thunk {
+    pub(crate) fn new(ctx: NormalizationContext, e: InputSubExpr) -> Thunk {
+        ThunkInternal::Unnormalized(ctx, e).into_thunk()
+    }
+
+    pub(crate) fn from_value(v: Value) -> Thunk {
+        ThunkInternal::Value(WHNF, v).into_thunk()
+    }
+
+    pub(crate) fn from_normalized_expr(e: OutputSubExpr) -> Thunk {
+        Thunk::new(NormalizationContext::new(), e.embed_absurd().note_absurd())
+    }
+
+    // Normalizes contents to normal form; faster than `normalize_nf` if
+    // no one else shares this thunk
+    pub(crate) fn normalize_mut(&mut self) {
+        match Rc::get_mut(&mut self.0) {
+            // Mutate directly if sole owner
+            Some(refcell) => RefCell::get_mut(refcell).normalize_nf(),
+            // Otherwise mutate through the refcell
+            None => self.0.borrow_mut().normalize_nf(),
+        }
+    }
+
+    fn do_normalize_whnf(&self) {
+        let borrow = self.0.borrow();
+        match &*borrow {
+            ThunkInternal::Unnormalized(_, _) => {
+                drop(borrow);
+                self.0.borrow_mut().normalize_whnf();
+            }
+            // Already at least in WHNF
+            ThunkInternal::Value(_, _) => {}
+        }
+    }
+
+    fn do_normalize_nf(&self) {
+        let borrow = self.0.borrow();
+        match &*borrow {
+            ThunkInternal::Unnormalized(_, _)
+            | ThunkInternal::Value(WHNF, _) => {
+                drop(borrow);
+                self.0.borrow_mut().normalize_nf();
+            }
+            // Already in NF
+            ThunkInternal::Value(NF, _) => {}
+        }
+    }
+
+    // WARNING: avoid normalizing any thunk while holding on to this ref
+    // or you could run into BorrowMut panics
+    pub(crate) fn normalize_nf(&self) -> Ref<Value> {
+        self.do_normalize_nf();
+        Ref::map(self.0.borrow(), ThunkInternal::as_nf)
+    }
+
+    // WARNING: avoid normalizing any thunk while holding on to this ref
+    // or you could run into BorrowMut panics
+    pub(crate) fn as_value(&self) -> Ref<Value> {
+        self.do_normalize_whnf();
+        Ref::map(self.0.borrow(), ThunkInternal::as_whnf)
+    }
+
+    pub(crate) fn to_value(&self) -> Value {
+        self.as_value().clone()
+    }
+
+    pub(crate) fn normalize_to_expr(&self) -> OutputSubExpr {
+        self.normalize_to_expr_maybe_alpha(false)
+    }
+
+    pub(crate) fn normalize_to_expr_maybe_alpha(
+        &self,
+        alpha: bool,
+    ) -> OutputSubExpr {
+        self.normalize_nf().normalize_to_expr_maybe_alpha(alpha)
+    }
+
+    pub(crate) fn app_val(&self, val: Value) -> Value {
+        self.app_thunk(val.into_thunk())
+    }
+
+    pub(crate) fn app_thunk(&self, th: Thunk) -> Value {
+        apply_any(self.clone(), th)
+    }
+
+    pub(crate) fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
+        self.0.borrow().shift(delta, var).into_thunk()
+    }
+
+    pub(crate) fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self {
+        self.0.borrow().subst_shift(var, val).into_thunk()
+    }
+}
+
+impl TypeThunk {
+    pub(crate) fn from_value(v: Value) -> TypeThunk {
+        TypeThunk::from_thunk(Thunk::from_value(v))
+    }
+
+    pub(crate) fn from_thunk(th: Thunk) -> TypeThunk {
+        TypeThunk::Thunk(th)
+    }
+
+    pub(crate) fn from_type(t: Type) -> TypeThunk {
+        TypeThunk::Type(t)
+    }
+
+    pub(crate) fn normalize_mut(&mut self) {
+        match self {
+            TypeThunk::Thunk(th) => th.normalize_mut(),
+            TypeThunk::Type(_) => {}
+        }
+    }
+
+    pub(crate) fn normalize_nf(&self) -> Value {
+        match self {
+            TypeThunk::Thunk(th) => th.normalize_nf().clone(),
+            TypeThunk::Type(t) => t.to_value().normalize(),
+        }
+    }
+
+    pub(crate) fn to_value(&self) -> Value {
+        match self {
+            TypeThunk::Thunk(th) => th.to_value(),
+            TypeThunk::Type(t) => t.to_value(),
+        }
+    }
+
+    pub(crate) fn to_type(
+        &self,
+        ctx: &TypecheckContext,
+    ) -> Result<Type, TypeError> {
+        match self {
+            TypeThunk::Type(t) => Ok(t.clone()),
+            TypeThunk::Thunk(th) => {
+                // TODO: rule out statically
+                mktype(ctx, th.normalize_to_expr().embed_absurd().note_absurd())
+            }
+        }
+    }
+
+    pub(crate) fn normalize_to_expr_maybe_alpha(
+        &self,
+        alpha: bool,
+    ) -> OutputSubExpr {
+        self.normalize_nf().normalize_to_expr_maybe_alpha(alpha)
+    }
+
+    pub(crate) fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
+        match self {
+            TypeThunk::Thunk(th) => TypeThunk::Thunk(th.shift(delta, var)),
+            TypeThunk::Type(t) => TypeThunk::Type(t.shift(delta, var)),
+        }
+    }
+
+    pub(crate) fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self {
+        match self {
+            TypeThunk::Thunk(th) => TypeThunk::Thunk(th.subst_shift(var, val)),
+            TypeThunk::Type(t) => TypeThunk::Type(t.subst_shift(var, val)),
+        }
+    }
+}
+
+impl std::cmp::PartialEq for Thunk {
+    fn eq(&self, other: &Self) -> bool {
+        &*self.as_value() == &*other.as_value()
+    }
+}
+impl std::cmp::Eq for Thunk {}
+
+impl std::cmp::PartialEq for TypeThunk {
+    fn eq(&self, other: &Self) -> bool {
+        self.to_value() == other.to_value()
+    }
+}
+impl std::cmp::Eq for TypeThunk {}
diff --git a/dhall/src/core/value.rs b/dhall/src/core/value.rs
new file mode 100644
index 0000000..31193d2
--- /dev/null
+++ b/dhall/src/core/value.rs
@@ -0,0 +1,616 @@
+use std::collections::BTreeMap;
+
+use dhall_proc_macros as dhall;
+use dhall_syntax::{
+    rc, Builtin, Const, ExprF, Integer, InterpolatedTextContents, Label,
+    Natural, V, X,
+};
+
+use crate::core::thunk::{Thunk, TypeThunk};
+use crate::phase::normalize::{
+    apply_builtin, normalize_one_layer, squash_textlit, OutputSubExpr,
+};
+use crate::phase::Typed;
+
+/// Stores a pair of variables: a normal one and if relevant one
+/// that corresponds to the alpha-normalized version of the first one.
+/// Equality is up to alpha-equivalence.
+#[derive(Debug, Clone, Eq)]
+pub(crate) struct AlphaVar {
+    normal: V<Label>,
+    alpha: Option<V<()>>,
+}
+
+// Exactly like a Label, but equality returns always true.
+// This is so that Value equality is exactly alpha-equivalence.
+#[derive(Debug, Clone, Eq)]
+pub(crate) struct AlphaLabel(Label);
+
+/// A semantic value.
+/// Equality is up to alpha-equivalence (renaming of bound variables)
+/// and beta-equivalence (normalization).
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(crate) enum Value {
+    /// Closures
+    Lam(AlphaLabel, Thunk, Thunk),
+    AppliedBuiltin(Builtin, Vec<Thunk>),
+    /// `λ(x: a) -> Some x`
+    OptionalSomeClosure(TypeThunk),
+    /// `λ(x : a) -> λ(xs : List a) -> [ x ] # xs`
+    /// `λ(xs : List a) -> [ x ] # xs`
+    ListConsClosure(TypeThunk, Option<Thunk>),
+    /// `λ(x : Natural) -> x + 1`
+    NaturalSuccClosure,
+    Pi(AlphaLabel, TypeThunk, TypeThunk),
+
+    Var(AlphaVar),
+    Const(Const),
+    BoolLit(bool),
+    NaturalLit(Natural),
+    IntegerLit(Integer),
+    EmptyOptionalLit(TypeThunk),
+    NEOptionalLit(Thunk),
+    EmptyListLit(TypeThunk),
+    NEListLit(Vec<Thunk>),
+    RecordLit(BTreeMap<Label, Thunk>),
+    RecordType(BTreeMap<Label, TypeThunk>),
+    UnionType(BTreeMap<Label, Option<TypeThunk>>),
+    UnionConstructor(Label, BTreeMap<Label, Option<TypeThunk>>),
+    UnionLit(Label, Thunk, BTreeMap<Label, Option<TypeThunk>>),
+    TextLit(Vec<InterpolatedTextContents<Thunk>>),
+    /// Invariant: This must not contain a value captured by one of the variants above.
+    PartialExpr(ExprF<Thunk, Label, X>),
+}
+
+impl AlphaVar {
+    pub(crate) fn to_var(&self, alpha: bool) -> V<Label> {
+        match (alpha, &self.alpha) {
+            (true, Some(x)) => V("_".into(), x.1),
+            _ => self.normal.clone(),
+        }
+    }
+    pub(crate) fn from_var(normal: V<Label>) -> Self {
+        AlphaVar {
+            normal,
+            alpha: None,
+        }
+    }
+    pub(crate) fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
+        AlphaVar {
+            normal: self.normal.shift(delta, &var.normal),
+            alpha: match (&self.alpha, &var.alpha) {
+                (Some(x), Some(v)) => Some(x.shift(delta, v)),
+                _ => None,
+            },
+        }
+    }
+}
+
+impl AlphaLabel {
+    fn to_label_maybe_alpha(&self, alpha: bool) -> Label {
+        if alpha {
+            "_".into()
+        } else {
+            self.to_label()
+        }
+    }
+    fn to_label(&self) -> Label {
+        self.clone().into()
+    }
+}
+
+impl Value {
+    pub(crate) fn into_thunk(self) -> Thunk {
+        Thunk::from_value(self)
+    }
+
+    /// Convert the value to a fully normalized syntactic expression
+    pub(crate) fn normalize_to_expr(&self) -> OutputSubExpr {
+        self.normalize_to_expr_maybe_alpha(false)
+    }
+    /// Convert the value to a fully normalized syntactic expression. Also alpha-normalize
+    /// if alpha is `true`
+    pub(crate) fn normalize_to_expr_maybe_alpha(
+        &self,
+        alpha: bool,
+    ) -> OutputSubExpr {
+        match self {
+            Value::Lam(x, t, e) => rc(ExprF::Lam(
+                x.to_label_maybe_alpha(alpha),
+                t.normalize_to_expr_maybe_alpha(alpha),
+                e.normalize_to_expr_maybe_alpha(alpha),
+            )),
+            Value::AppliedBuiltin(b, args) => {
+                let mut e = rc(ExprF::Builtin(*b));
+                for v in args {
+                    e = rc(ExprF::App(
+                        e,
+                        v.normalize_to_expr_maybe_alpha(alpha),
+                    ));
+                }
+                e
+            }
+            Value::OptionalSomeClosure(n) => {
+                let a = n.normalize_to_expr_maybe_alpha(alpha);
+                dhall::subexpr!(λ(x: a) -> Some x)
+            }
+            Value::ListConsClosure(a, None) => {
+                // Avoid accidental capture of the new `x` variable
+                let a1 = a.shift(1, &Label::from("x").into());
+                let a1 = a1.normalize_to_expr_maybe_alpha(alpha);
+                let a = a.normalize_to_expr_maybe_alpha(alpha);
+                dhall::subexpr!(λ(x : a) -> λ(xs : List a1) -> [ x ] # xs)
+            }
+            Value::ListConsClosure(n, Some(v)) => {
+                // Avoid accidental capture of the new `xs` variable
+                let v = v.shift(1, &Label::from("xs").into());
+                let v = v.normalize_to_expr_maybe_alpha(alpha);
+                let a = n.normalize_to_expr_maybe_alpha(alpha);
+                dhall::subexpr!(λ(xs : List a) -> [ v ] # xs)
+            }
+            Value::NaturalSuccClosure => {
+                dhall::subexpr!(λ(x : Natural) -> x + 1)
+            }
+            Value::Pi(x, t, e) => rc(ExprF::Pi(
+                x.to_label_maybe_alpha(alpha),
+                t.normalize_to_expr_maybe_alpha(alpha),
+                e.normalize_to_expr_maybe_alpha(alpha),
+            )),
+            Value::Var(v) => rc(ExprF::Var(v.to_var(alpha))),
+            Value::Const(c) => rc(ExprF::Const(*c)),
+            Value::BoolLit(b) => rc(ExprF::BoolLit(*b)),
+            Value::NaturalLit(n) => rc(ExprF::NaturalLit(*n)),
+            Value::IntegerLit(n) => rc(ExprF::IntegerLit(*n)),
+            Value::EmptyOptionalLit(n) => rc(ExprF::App(
+                rc(ExprF::Builtin(Builtin::OptionalNone)),
+                n.normalize_to_expr_maybe_alpha(alpha),
+            )),
+            Value::NEOptionalLit(n) => {
+                rc(ExprF::SomeLit(n.normalize_to_expr_maybe_alpha(alpha)))
+            }
+            Value::EmptyListLit(n) => {
+                rc(ExprF::EmptyListLit(n.normalize_to_expr_maybe_alpha(alpha)))
+            }
+            Value::NEListLit(elts) => rc(ExprF::NEListLit(
+                elts.into_iter()
+                    .map(|n| n.normalize_to_expr_maybe_alpha(alpha))
+                    .collect(),
+            )),
+            Value::RecordLit(kvs) => rc(ExprF::RecordLit(
+                kvs.iter()
+                    .map(|(k, v)| {
+                        (k.clone(), v.normalize_to_expr_maybe_alpha(alpha))
+                    })
+                    .collect(),
+            )),
+            Value::RecordType(kts) => rc(ExprF::RecordType(
+                kts.iter()
+                    .map(|(k, v)| {
+                        (k.clone(), v.normalize_to_expr_maybe_alpha(alpha))
+                    })
+                    .collect(),
+            )),
+            Value::UnionType(kts) => rc(ExprF::UnionType(
+                kts.iter()
+                    .map(|(k, v)| {
+                        (
+                            k.clone(),
+                            v.as_ref().map(|v| {
+                                v.normalize_to_expr_maybe_alpha(alpha)
+                            }),
+                        )
+                    })
+                    .collect(),
+            )),
+            Value::UnionConstructor(l, kts) => {
+                let kts = kts
+                    .iter()
+                    .map(|(k, v)| {
+                        (
+                            k.clone(),
+                            v.as_ref().map(|v| {
+                                v.normalize_to_expr_maybe_alpha(alpha)
+                            }),
+                        )
+                    })
+                    .collect();
+                rc(ExprF::Field(rc(ExprF::UnionType(kts)), l.clone()))
+            }
+            Value::UnionLit(l, v, kts) => rc(ExprF::UnionLit(
+                l.clone(),
+                v.normalize_to_expr_maybe_alpha(alpha),
+                kts.iter()
+                    .map(|(k, v)| {
+                        (
+                            k.clone(),
+                            v.as_ref().map(|v| {
+                                v.normalize_to_expr_maybe_alpha(alpha)
+                            }),
+                        )
+                    })
+                    .collect(),
+            )),
+            Value::TextLit(elts) => {
+                use InterpolatedTextContents::{Expr, Text};
+                rc(ExprF::TextLit(
+                    elts.iter()
+                        .map(|contents| match contents {
+                            Expr(e) => {
+                                Expr(e.normalize_to_expr_maybe_alpha(alpha))
+                            }
+                            Text(s) => Text(s.clone()),
+                        })
+                        .collect(),
+                ))
+            }
+            Value::PartialExpr(e) => {
+                rc(e.map_ref_simple(|v| v.normalize_to_expr_maybe_alpha(alpha)))
+            }
+        }
+    }
+
+    // Deprecated
+    pub(crate) fn normalize(&self) -> Value {
+        let mut v = self.clone();
+        v.normalize_mut();
+        v
+    }
+
+    pub(crate) fn normalize_mut(&mut self) {
+        match self {
+            Value::NaturalSuccClosure
+            | Value::Var(_)
+            | Value::Const(_)
+            | Value::BoolLit(_)
+            | Value::NaturalLit(_)
+            | Value::IntegerLit(_) => {}
+
+            Value::EmptyOptionalLit(tth)
+            | Value::OptionalSomeClosure(tth)
+            | Value::EmptyListLit(tth) => {
+                tth.normalize_mut();
+            }
+
+            Value::NEOptionalLit(th) => {
+                th.normalize_mut();
+            }
+            Value::Lam(_, t, e) => {
+                t.normalize_mut();
+                e.normalize_mut();
+            }
+            Value::Pi(_, t, e) => {
+                t.normalize_mut();
+                e.normalize_mut();
+            }
+            Value::AppliedBuiltin(_, args) => {
+                for x in args.iter_mut() {
+                    x.normalize_mut();
+                }
+            }
+            Value::ListConsClosure(t, v) => {
+                t.normalize_mut();
+                for x in v.iter_mut() {
+                    x.normalize_mut();
+                }
+            }
+            Value::NEListLit(elts) => {
+                for x in elts.iter_mut() {
+                    x.normalize_mut();
+                }
+            }
+            Value::RecordLit(kvs) => {
+                for x in kvs.values_mut() {
+                    x.normalize_mut();
+                }
+            }
+            Value::RecordType(kvs) => {
+                for x in kvs.values_mut() {
+                    x.normalize_mut();
+                }
+            }
+            Value::UnionType(kts) | Value::UnionConstructor(_, kts) => {
+                for x in kts.values_mut().flat_map(|opt| opt) {
+                    x.normalize_mut();
+                }
+            }
+            Value::UnionLit(_, v, kts) => {
+                v.normalize_mut();
+                for x in kts.values_mut().flat_map(|opt| opt) {
+                    x.normalize_mut();
+                }
+            }
+            Value::TextLit(elts) => {
+                for x in elts.iter_mut() {
+                    use InterpolatedTextContents::{Expr, Text};
+                    match x {
+                        Expr(n) => n.normalize_mut(),
+                        Text(_) => {}
+                    }
+                }
+            }
+            Value::PartialExpr(e) => {
+                // TODO: need map_mut_simple
+                e.map_ref_simple(|v| {
+                    v.normalize_nf();
+                });
+            }
+        }
+    }
+
+    /// Apply to a value
+    pub(crate) fn app(self, val: Value) -> Value {
+        self.app_val(val)
+    }
+
+    /// Apply to a value
+    pub(crate) fn app_val(self, val: Value) -> Value {
+        self.app_thunk(val.into_thunk())
+    }
+
+    /// Apply to a thunk
+    pub(crate) fn app_thunk(self, th: Thunk) -> Value {
+        Thunk::from_value(self).app_thunk(th)
+    }
+
+    pub(crate) fn from_builtin(b: Builtin) -> Value {
+        Value::AppliedBuiltin(b, vec![])
+    }
+
+    pub(crate) fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
+        match self {
+            Value::Lam(x, t, e) => Value::Lam(
+                x.clone(),
+                t.shift(delta, var),
+                e.shift(delta, &var.shift(1, &x.into())),
+            ),
+            Value::AppliedBuiltin(b, args) => Value::AppliedBuiltin(
+                *b,
+                args.iter().map(|v| v.shift(delta, var)).collect(),
+            ),
+            Value::NaturalSuccClosure => Value::NaturalSuccClosure,
+            Value::OptionalSomeClosure(tth) => {
+                Value::OptionalSomeClosure(tth.shift(delta, var))
+            }
+            Value::ListConsClosure(t, v) => Value::ListConsClosure(
+                t.shift(delta, var),
+                v.as_ref().map(|v| v.shift(delta, var)),
+            ),
+            Value::Pi(x, t, e) => Value::Pi(
+                x.clone(),
+                t.shift(delta, var),
+                e.shift(delta, &var.shift(1, &x.into())),
+            ),
+            Value::Var(v) => Value::Var(v.shift(delta, var)),
+            Value::Const(c) => Value::Const(*c),
+            Value::BoolLit(b) => Value::BoolLit(*b),
+            Value::NaturalLit(n) => Value::NaturalLit(*n),
+            Value::IntegerLit(n) => Value::IntegerLit(*n),
+            Value::EmptyOptionalLit(tth) => {
+                Value::EmptyOptionalLit(tth.shift(delta, var))
+            }
+            Value::NEOptionalLit(th) => {
+                Value::NEOptionalLit(th.shift(delta, var))
+            }
+            Value::EmptyListLit(tth) => {
+                Value::EmptyListLit(tth.shift(delta, var))
+            }
+            Value::NEListLit(elts) => Value::NEListLit(
+                elts.iter().map(|v| v.shift(delta, var)).collect(),
+            ),
+            Value::RecordLit(kvs) => Value::RecordLit(
+                kvs.iter()
+                    .map(|(k, v)| (k.clone(), v.shift(delta, var)))
+                    .collect(),
+            ),
+            Value::RecordType(kvs) => Value::RecordType(
+                kvs.iter()
+                    .map(|(k, v)| (k.clone(), v.shift(delta, var)))
+                    .collect(),
+            ),
+            Value::UnionType(kts) => Value::UnionType(
+                kts.iter()
+                    .map(|(k, v)| {
+                        (k.clone(), v.as_ref().map(|v| v.shift(delta, var)))
+                    })
+                    .collect(),
+            ),
+            Value::UnionConstructor(x, kts) => Value::UnionConstructor(
+                x.clone(),
+                kts.iter()
+                    .map(|(k, v)| {
+                        (k.clone(), v.as_ref().map(|v| v.shift(delta, var)))
+                    })
+                    .collect(),
+            ),
+            Value::UnionLit(x, v, kts) => Value::UnionLit(
+                x.clone(),
+                v.shift(delta, var),
+                kts.iter()
+                    .map(|(k, v)| {
+                        (k.clone(), v.as_ref().map(|v| v.shift(delta, var)))
+                    })
+                    .collect(),
+            ),
+            Value::TextLit(elts) => Value::TextLit(
+                elts.iter()
+                    .map(|contents| {
+                        use InterpolatedTextContents::{Expr, Text};
+                        match contents {
+                            Expr(th) => Expr(th.shift(delta, var)),
+                            Text(s) => Text(s.clone()),
+                        }
+                    })
+                    .collect(),
+            ),
+            Value::PartialExpr(e) => {
+                Value::PartialExpr(e.map_ref_with_special_handling_of_binders(
+                    |v| v.shift(delta, var),
+                    |x, v| v.shift(delta, &var.shift(1, &x.into())),
+                    X::clone,
+                    Label::clone,
+                ))
+            }
+        }
+    }
+
+    pub(crate) fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self {
+        match self {
+            // Retry normalizing since substituting may allow progress
+            Value::AppliedBuiltin(b, args) => apply_builtin(
+                *b,
+                args.iter().map(|v| v.subst_shift(var, val)).collect(),
+            ),
+            // Retry normalizing since substituting may allow progress
+            Value::PartialExpr(e) => {
+                normalize_one_layer(e.map_ref_with_special_handling_of_binders(
+                    |v| v.subst_shift(var, val),
+                    |x, v| {
+                        v.subst_shift(
+                            &var.shift(1, &x.into()),
+                            &val.shift(1, &x.into()),
+                        )
+                    },
+                    X::clone,
+                    Label::clone,
+                ))
+            }
+            // Retry normalizing since substituting may allow progress
+            Value::TextLit(elts) => {
+                Value::TextLit(squash_textlit(elts.iter().map(|contents| {
+                    use InterpolatedTextContents::{Expr, Text};
+                    match contents {
+                        Expr(th) => Expr(th.subst_shift(var, val)),
+                        Text(s) => Text(s.clone()),
+                    }
+                })))
+            }
+            Value::Lam(x, t, e) => Value::Lam(
+                x.clone(),
+                t.subst_shift(var, val),
+                e.subst_shift(
+                    &var.shift(1, &x.into()),
+                    &val.shift(1, &x.into()),
+                ),
+            ),
+            Value::NaturalSuccClosure => Value::NaturalSuccClosure,
+            Value::OptionalSomeClosure(tth) => {
+                Value::OptionalSomeClosure(tth.subst_shift(var, val))
+            }
+            Value::ListConsClosure(t, v) => Value::ListConsClosure(
+                t.subst_shift(var, val),
+                v.as_ref().map(|v| v.subst_shift(var, val)),
+            ),
+            Value::Pi(x, t, e) => Value::Pi(
+                x.clone(),
+                t.subst_shift(var, val),
+                e.subst_shift(
+                    &var.shift(1, &x.into()),
+                    &val.shift(1, &x.into()),
+                ),
+            ),
+            Value::Var(v) if v == var => val.to_value().clone(),
+            Value::Var(v) => Value::Var(v.shift(-1, var)),
+            Value::Const(c) => Value::Const(*c),
+            Value::BoolLit(b) => Value::BoolLit(*b),
+            Value::NaturalLit(n) => Value::NaturalLit(*n),
+            Value::IntegerLit(n) => Value::IntegerLit(*n),
+            Value::EmptyOptionalLit(tth) => {
+                Value::EmptyOptionalLit(tth.subst_shift(var, val))
+            }
+            Value::NEOptionalLit(th) => {
+                Value::NEOptionalLit(th.subst_shift(var, val))
+            }
+            Value::EmptyListLit(tth) => {
+                Value::EmptyListLit(tth.subst_shift(var, val))
+            }
+            Value::NEListLit(elts) => Value::NEListLit(
+                elts.iter().map(|v| v.subst_shift(var, val)).collect(),
+            ),
+            Value::RecordLit(kvs) => Value::RecordLit(
+                kvs.iter()
+                    .map(|(k, v)| (k.clone(), v.subst_shift(var, val)))
+                    .collect(),
+            ),
+            Value::RecordType(kvs) => Value::RecordType(
+                kvs.iter()
+                    .map(|(k, v)| (k.clone(), v.subst_shift(var, val)))
+                    .collect(),
+            ),
+            Value::UnionType(kts) => Value::UnionType(
+                kts.iter()
+                    .map(|(k, v)| {
+                        (k.clone(), v.as_ref().map(|v| v.subst_shift(var, val)))
+                    })
+                    .collect(),
+            ),
+            Value::UnionConstructor(x, kts) => Value::UnionConstructor(
+                x.clone(),
+                kts.iter()
+                    .map(|(k, v)| {
+                        (k.clone(), v.as_ref().map(|v| v.subst_shift(var, val)))
+                    })
+                    .collect(),
+            ),
+            Value::UnionLit(x, v, kts) => Value::UnionLit(
+                x.clone(),
+                v.subst_shift(var, val),
+                kts.iter()
+                    .map(|(k, v)| {
+                        (k.clone(), v.as_ref().map(|v| v.subst_shift(var, val)))
+                    })
+                    .collect(),
+            ),
+        }
+    }
+}
+
+impl std::cmp::PartialEq for AlphaVar {
+    fn eq(&self, other: &Self) -> bool {
+        match (&self.alpha, &other.alpha) {
+            (Some(x), Some(y)) => x == y,
+            (None, None) => self.normal == other.normal,
+            _ => false,
+        }
+    }
+}
+impl std::cmp::PartialEq for AlphaLabel {
+    fn eq(&self, _other: &Self) -> bool {
+        true
+    }
+}
+
+impl From<Label> for AlphaVar {
+    fn from(x: Label) -> AlphaVar {
+        AlphaVar {
+            normal: V(x, 0),
+            alpha: Some(V((), 0)),
+        }
+    }
+}
+impl<'a> From<&'a Label> for AlphaVar {
+    fn from(x: &'a Label) -> AlphaVar {
+        x.clone().into()
+    }
+}
+impl From<AlphaLabel> for AlphaVar {
+    fn from(x: AlphaLabel) -> AlphaVar {
+        let l: Label = x.into();
+        l.into()
+    }
+}
+impl<'a> From<&'a AlphaLabel> for AlphaVar {
+    fn from(x: &'a AlphaLabel) -> AlphaVar {
+        x.clone().into()
+    }
+}
+
+impl From<Label> for AlphaLabel {
+    fn from(x: Label) -> AlphaLabel {
+        AlphaLabel(x)
+    }
+}
+impl From<AlphaLabel> for Label {
+    fn from(x: AlphaLabel) -> Label {
+        x.0
+    }
+}