1 files changed, 167 insertions, 0 deletions
diff --git a/dhall/src/semantics/nze/visitor.rs b/dhall/src/semantics/nze/visitor.rs
new file mode 100644
index 0000000..d1a85d8
--- /dev/null
+++ b/dhall/src/semantics/nze/visitor.rs
@@ -0,0 +1,167 @@
+use std::iter::FromIterator;
+
+use crate::semantics::{Binder, BuiltinClosure, ValueKind};
+use crate::syntax::Label;
+
+/// A visitor trait that can be used to traverse `ValueKind`s. We need this pattern so that Rust lets
+/// us have as much mutability as we can. See the equivalent file in `crate::syntax` for more
+/// details.
+pub(crate) trait ValueKindVisitor<'a, V1, V2>: Sized {
+    type Error;
+
+    fn visit_val(&mut self, val: &'a V1) -> Result<V2, Self::Error>;
+    fn visit_binder(
+        mut self,
+        _label: &'a Binder,
+        ty: &'a V1,
+        val: &'a V1,
+    ) -> Result<(V2, V2), Self::Error> {
+        Ok((self.visit_val(ty)?, self.visit_val(val)?))
+    }
+    fn visit_vec(&mut self, x: &'a [V1]) -> Result<Vec<V2>, Self::Error> {
+        x.iter().map(|e| self.visit_val(e)).collect()
+    }
+    fn visit_opt(
+        &mut self,
+        x: &'a Option<V1>,
+    ) -> Result<Option<V2>, Self::Error> {
+        Ok(match x {
+            Some(x) => Some(self.visit_val(x)?),
+            None => None,
+        })
+    }
+    fn visit_map<T>(
+        &mut self,
+        x: impl IntoIterator<Item = (&'a Label, &'a V1)>,
+    ) -> Result<T, Self::Error>
+    where
+        V1: 'a,
+        T: FromIterator<(Label, V2)>,
+    {
+        x.into_iter()
+            .map(|(k, x)| Ok((k.clone(), self.visit_val(x)?)))
+            .collect()
+    }
+    fn visit_optmap<T>(
+        &mut self,
+        x: impl IntoIterator<Item = (&'a Label, &'a Option<V1>)>,
+    ) -> Result<T, Self::Error>
+    where
+        V1: 'a,
+        T: FromIterator<(Label, Option<V2>)>,
+    {
+        x.into_iter()
+            .map(|(k, x)| Ok((k.clone(), self.visit_opt(x)?)))
+            .collect()
+    }
+
+    fn visit(
+        self,
+        input: &'a ValueKind<V1>,
+    ) -> Result<ValueKind<V2>, Self::Error> {
+        visit_ref(self, input)
+    }
+}
+
+fn visit_ref<'a, Visitor, V1, V2>(
+    mut v: Visitor,
+    input: &'a ValueKind<V1>,
+) -> Result<ValueKind<V2>, Visitor::Error>
+where
+    Visitor: ValueKindVisitor<'a, V1, V2>,
+{
+    use ValueKind::*;
+    Ok(match input {
+        LamClosure {
+            binder,
+            annot,
+            closure,
+        } => LamClosure {
+            binder: binder.clone(),
+            annot: v.visit_val(annot)?,
+            closure: closure.clone(),
+        },
+        PiClosure {
+            binder,
+            annot,
+            closure,
+        } => PiClosure {
+            binder: binder.clone(),
+            annot: v.visit_val(annot)?,
+            closure: closure.clone(),
+        },
+        AppliedBuiltin(BuiltinClosure {
+            b,
+            args,
+            types,
+            env,
+        }) => AppliedBuiltin(BuiltinClosure {
+            b: *b,
+            args: v.visit_vec(args)?,
+            types: v.visit_vec(types)?,
+            env: env.clone(),
+        }),
+        Var(v) => Var(*v),
+        Const(k) => Const(*k),
+        BoolLit(b) => BoolLit(*b),
+        NaturalLit(n) => NaturalLit(*n),
+        IntegerLit(n) => IntegerLit(*n),
+        DoubleLit(n) => DoubleLit(*n),
+        EmptyOptionalLit(t) => EmptyOptionalLit(v.visit_val(t)?),
+        NEOptionalLit(x) => NEOptionalLit(v.visit_val(x)?),
+        EmptyListLit(t) => EmptyListLit(v.visit_val(t)?),
+        NEListLit(xs) => NEListLit(v.visit_vec(xs)?),
+        RecordType(kts) => RecordType(v.visit_map(kts)?),
+        RecordLit(kvs) => RecordLit(v.visit_map(kvs)?),
+        UnionType(kts) => UnionType(v.visit_optmap(kts)?),
+        UnionConstructor(l, kts, uniont) => UnionConstructor(
+            l.clone(),
+            v.visit_optmap(kts)?,
+            v.visit_val(uniont)?,
+        ),
+        UnionLit(l, x, kts, uniont, ctort) => UnionLit(
+            l.clone(),
+            v.visit_val(x)?,
+            v.visit_optmap(kts)?,
+            v.visit_val(uniont)?,
+            v.visit_val(ctort)?,
+        ),
+        TextLit(ts) => TextLit(
+            ts.iter()
+                .map(|t| t.traverse_ref(|e| v.visit_val(e)))
+                .collect::<Result<_, _>>()?,
+        ),
+        Equivalence(x, y) => Equivalence(v.visit_val(x)?, v.visit_val(y)?),
+        PartialExpr(e) => PartialExpr(e.traverse_ref(|e| v.visit_val(e))?),
+        Thunk(th) => Thunk(th.clone()),
+    })
+}
+
+pub struct TraverseRefWithBindersVisitor<F1, F2> {
+    pub visit_val: F1,
+    pub visit_under_binder: F2,
+}
+
+impl<'a, V1, V2, Err, F1, F2> ValueKindVisitor<'a, V1, V2>
+    for TraverseRefWithBindersVisitor<F1, F2>
+where
+    V1: 'a,
+    F1: FnMut(&'a V1) -> Result<V2, Err>,
+    F2: for<'b> FnOnce(&'a Binder, &'b V1, &'a V1) -> Result<V2, Err>,
+{
+    type Error = Err;
+
+    fn visit_val(&mut self, val: &'a V1) -> Result<V2, Self::Error> {
+        (self.visit_val)(val)
+    }
+    fn visit_binder<'b>(
+        mut self,
+        label: &'a Binder,
+        ty: &'a V1,
+        val: &'a V1,
+    ) -> Result<(V2, V2), Self::Error> {
+        let val = (self.visit_under_binder)(label, ty, val)?;
+        let ty = (self.visit_val)(ty)?;
+        Ok((ty, val))
+    }
+}