Upgrade map to traverse

2 files changed, 102 insertions, 46 deletions

diff --git a/dhall_core/src/core.rs b/dhall_core/src/core.rs
index a9033f3..355f625 100644
--- a/dhall_core/src/core.rs
+++ b/dhall_core/src/core.rs
@@ -12,6 +12,13 @@ pub type Double = NaiveDouble;
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
 pub enum X {}
 
+pub fn trivial_result<T>(x: Result<T, X>) -> T {
+    match x {
+        Ok(x) => x,
+        Err(e) => match e {},
+    }
+}
+
 /// Double with bitwise equality
 #[derive(Debug, Copy, Clone)]
 pub struct NaiveDouble(f64);
@@ -362,83 +369,122 @@ impl<SE, L, N, E> ExprF<SE, L, N, E> {
     }
 
     #[inline(always)]
-    pub fn map<SE2, L2, N2, E2, F1, F2, F3, F4, F5>(
+    pub fn traverse<SE2, L2, N2, E2, Err, F1, F2, F3, F4, F5>(
         self,
         map_subexpr: F1,
         map_under_binder: F2,
         map_note: F3,
         map_embed: F4,
         mut map_label: F5,
-    ) -> ExprF<SE2, L2, N2, E2>
+    ) -> Result<ExprF<SE2, L2, N2, E2>, Err>
     where
         L: Ord,
         L2: Ord,
-        F1: FnMut(SE) -> SE2,
-        F2: FnOnce(&L, SE) -> SE2,
-        F3: FnOnce(N) -> N2,
-        F4: FnOnce(E) -> E2,
-        F5: FnMut(L) -> L2,
+        F1: FnMut(SE) -> Result<SE2, Err>,
+        F2: FnOnce(&L, SE) -> Result<SE2, Err>,
+        F3: FnOnce(N) -> Result<N2, Err>,
+        F4: FnOnce(E) -> Result<E2, Err>,
+        F5: FnMut(L) -> Result<L2, Err>,
     {
         let mut map = map_subexpr;
-        fn vec<T, U, F: FnMut(T) -> U>(x: Vec<T>, f: F) -> Vec<U> {
+        fn vec<T, U, Err, F: FnMut(T) -> Result<U, Err>>(
+            x: Vec<T>,
+            f: F,
+        ) -> Result<Vec<U>, Err> {
             x.into_iter().map(f).collect()
         }
-        fn btmap<K, L, T, U, FK, FV>(
+        fn opt<T, U, Err, F: FnOnce(T) -> Result<U, Err>>(
+            x: Option<T>,
+            f: F,
+        ) -> Result<Option<U>, Err> {
+            Ok(match x {
+                Some(x) => Some(f(x)?),
+                None => None,
+            })
+        }
+        fn btmap<K, L, T, U, Err, FK, FV>(
             x: BTreeMap<K, T>,
             mut fk: FK,
             mut fv: FV,
-        ) -> BTreeMap<L, U>
+        ) -> Result<BTreeMap<L, U>, Err>
         where
             K: Ord,
             L: Ord,
-            FK: FnMut(K) -> L,
-            FV: FnMut(T) -> U,
+            FK: FnMut(K) -> Result<L, Err>,
+            FV: FnMut(T) -> Result<U, Err>,
         {
-            x.into_iter().map(|(k, v)| (fk(k), fv(v))).collect()
+            x.into_iter().map(|(k, v)| Ok((fk(k)?, fv(v)?))).collect()
         }
 
         use crate::ExprF::*;
-        match self {
-            Var(V(l, n)) => Var(V(map_label(l), n)),
+        Ok(match self {
+            Var(V(l, n)) => Var(V(map_label(l)?, n)),
             Lam(l, t, b) => {
-                let b = map_under_binder(&l, b);
-                Lam(map_label(l), map(t), b)
+                let b = map_under_binder(&l, b)?;
+                Lam(map_label(l)?, map(t)?, b)
             }
             Pi(l, t, b) => {
-                let b = map_under_binder(&l, b);
-                Pi(map_label(l), map(t), b)
+                let b = map_under_binder(&l, b)?;
+                Pi(map_label(l)?, map(t)?, b)
             }
             Let(l, t, a, b) => {
-                let b = map_under_binder(&l, b);
-                Let(map_label(l), t.map(&mut map), map(a), b)
+                let b = map_under_binder(&l, b)?;
+                Let(map_label(l)?, opt(t, &mut map)?, map(a)?, b)
             }
-            App(f, args) => App(map(f), vec(args, map)),
-            Annot(x, t) => Annot(map(x), map(t)),
+            App(f, args) => App(map(f)?, vec(args, map)?),
+            Annot(x, t) => Annot(map(x)?, map(t)?),
             Const(k) => Const(k),
             Builtin(v) => Builtin(v),
             BoolLit(b) => BoolLit(b),
             NaturalLit(n) => NaturalLit(n),
             IntegerLit(n) => IntegerLit(n),
             DoubleLit(n) => DoubleLit(n),
-            TextLit(t) => TextLit(t.map(map)),
-            BinOp(o, x, y) => BinOp(o, map(x), map(y)),
-            BoolIf(b, t, f) => BoolIf(map(b), map(t), map(f)),
-            EmptyListLit(t) => EmptyListLit(map(t)),
-            NEListLit(es) => NEListLit(vec(es, map)),
-            EmptyOptionalLit(t) => EmptyOptionalLit(map(t)),
-            NEOptionalLit(e) => NEOptionalLit(map(e)),
-            RecordType(kts) => RecordType(btmap(kts, map_label, map)),
-            RecordLit(kvs) => RecordLit(btmap(kvs, map_label, map)),
-            UnionType(kts) => UnionType(btmap(kts, map_label, map)),
+            TextLit(t) => TextLit(t.traverse(map)?),
+            BinOp(o, x, y) => BinOp(o, map(x)?, map(y)?),
+            BoolIf(b, t, f) => BoolIf(map(b)?, map(t)?, map(f)?),
+            EmptyListLit(t) => EmptyListLit(map(t)?),
+            NEListLit(es) => NEListLit(vec(es, map)?),
+            EmptyOptionalLit(t) => EmptyOptionalLit(map(t)?),
+            NEOptionalLit(e) => NEOptionalLit(map(e)?),
+            RecordType(kts) => RecordType(btmap(kts, map_label, map)?),
+            RecordLit(kvs) => RecordLit(btmap(kvs, map_label, map)?),
+            UnionType(kts) => UnionType(btmap(kts, map_label, map)?),
             UnionLit(k, v, kvs) => {
-                UnionLit(map_label(k), map(v), btmap(kvs, map_label, map))
+                UnionLit(map_label(k)?, map(v)?, btmap(kvs, map_label, map)?)
             }
-            Merge(x, y, t) => Merge(map(x), map(y), t.map(map)),
-            Field(e, l) => Field(map(e), map_label(l)),
-            Projection(e, ls) => Projection(map(e), vec(ls, map_label)),
-            Note(n, e) => Note(map_note(n), map(e)),
-            Embed(a) => Embed(map_embed(a)),
-        }
+            Merge(x, y, t) => Merge(map(x)?, map(y)?, opt(t, map)?),
+            Field(e, l) => Field(map(e)?, map_label(l)?),
+            Projection(e, ls) => Projection(map(e)?, vec(ls, map_label)?),
+            Note(n, e) => Note(map_note(n)?, map(e)?),
+            Embed(a) => Embed(map_embed(a)?),
+        })
+    }
+
+    #[inline(always)]
+    pub fn map<SE2, L2, N2, E2, F1, F2, F3, F4, F5>(
+        self,
+        mut map_subexpr: F1,
+        map_under_binder: F2,
+        map_note: F3,
+        map_embed: F4,
+        mut map_label: F5,
+    ) -> ExprF<SE2, L2, N2, E2>
+    where
+        L: Ord,
+        L2: Ord,
+        F1: FnMut(SE) -> SE2,
+        F2: FnOnce(&L, SE) -> SE2,
+        F3: FnOnce(N) -> N2,
+        F4: FnOnce(E) -> E2,
+        F5: FnMut(L) -> L2,
+    {
+        trivial_result(self.traverse(
+            |x| Ok(map_subexpr(x)),
+            |l, x| Ok(map_under_binder(l, x)),
+            |x| Ok(map_note(x)),
+            |x| Ok(map_embed(x)),
+            |x| Ok(map_label(x)),
+        ))
     }
 
     #[inline(always)]
diff --git a/dhall_core/src/text.rs b/dhall_core/src/text.rs
index 9500f32..7c0e2b4 100644
--- a/dhall_core/src/text.rs
+++ b/dhall_core/src/text.rs
@@ -34,18 +34,28 @@ pub enum InterpolatedTextContents<SubExpr> {
 }
 
 impl<SubExpr> InterpolatedText<SubExpr> {
-    pub fn map<SubExpr2, F>(self, mut f: F) -> InterpolatedText<SubExpr2>
+    pub fn traverse<SubExpr2, E, F>(
+        self,
+        mut f: F,
+    ) -> Result<InterpolatedText<SubExpr2>, E>
     where
-        F: FnMut(SubExpr) -> SubExpr2,
+        F: FnMut(SubExpr) -> Result<SubExpr2, E>,
     {
-        InterpolatedText {
+        Ok(InterpolatedText {
             head: self.head.clone(),
             tail: self
                 .tail
                 .into_iter()
-                .map(|(e, s)| (f(e), s.clone()))
-                .collect(),
-        }
+                .map(|(e, s)| Ok((f(e)?, s.clone())))
+                .collect::<Result<_, _>>()?,
+        })
+    }
+
+    pub fn map<SubExpr2, F>(self, mut f: F) -> InterpolatedText<SubExpr2>
+    where
+        F: FnMut(SubExpr) -> SubExpr2,
+    {
+        crate::trivial_result(self.traverse(|e| Ok(f(e))))
     }
 
     pub fn as_ref(&self) -> InterpolatedText<&SubExpr> {