Merge remote-tracking branch 'origin/master' into fintan/canonicalize

6 files changed, 646 insertions, 468 deletions

diff --git a/dhall_syntax/src/core/expr.rs b/dhall_syntax/src/core/expr.rs
index eeee4d8..2cb23c9 100644
--- a/dhall_syntax/src/core/expr.rs
+++ b/dhall_syntax/src/core/expr.rs
@@ -1,7 +1,7 @@
 use std::rc::Rc;
 
 use crate::map::{DupTreeMap, DupTreeSet};
-use crate::visitor;
+use crate::visitor::{self, ExprFMutVisitor, ExprFVisitor};
 use crate::*;
 
 pub type Integer = isize;
@@ -256,13 +256,6 @@ pub enum ExprF<SubExpr, Embed> {
 }
 
 impl<SE, E> ExprF<SE, E> {
-    pub(crate) fn visit<'a, V, Return>(&'a self, v: V) -> Return
-    where
-        V: visitor::GenericVisitor<&'a ExprF<SE, E>, Return>,
-    {
-        v.visit(self)
-    }
-
     pub fn traverse_ref_with_special_handling_of_binders<'a, SE2, Err>(
         &'a self,
         visit_subexpr: impl FnMut(&'a SE) -> Result<SE2, Err>,
@@ -271,10 +264,11 @@ impl<SE, E> ExprF<SE, E> {
     where
         E: Clone,
     {
-        self.visit(visitor::TraverseRefWithBindersVisitor {
+        visitor::TraverseRefWithBindersVisitor {
             visit_subexpr,
             visit_under_binder,
-        })
+        }
+        .visit(self)
     }
 
     fn traverse_ref<'a, SE2, Err>(
@@ -284,7 +278,14 @@ impl<SE, E> ExprF<SE, E> {
     where
         E: Clone,
     {
-        self.visit(visitor::TraverseRefVisitor { visit_subexpr })
+        visitor::TraverseRefVisitor { visit_subexpr }.visit(self)
+    }
+
+    fn traverse_mut<'a, Err>(
+        &'a mut self,
+        visit_subexpr: impl FnMut(&'a mut SE) -> Result<(), Err>,
+    ) -> Result<(), Err> {
+        visitor::TraverseMutVisitor { visit_subexpr }.visit(self)
     }
 
     pub fn map_ref_with_special_handling_of_binders<'a, SE2>(
@@ -310,38 +311,9 @@ impl<SE, E> ExprF<SE, E> {
     {
         trivial_result(self.traverse_ref(|x| Ok(map_subexpr(x))))
     }
-}
 
-impl<E> RawExpr<E> {
-    pub fn traverse_resolve<E2, Err>(
-        &self,
-        visit_import: impl FnMut(&Import<Expr<E2>>) -> Result<E2, Err>,
-    ) -> Result<RawExpr<E2>, Err> {
-        self.traverse_resolve_with_visitor(&mut visitor::ResolveVisitor(
-            visit_import,
-        ))
-    }
-
-    pub(crate) fn traverse_resolve_with_visitor<E2, Err, F1>(
-        &self,
-        visitor: &mut visitor::ResolveVisitor<F1>,
-    ) -> Result<RawExpr<E2>, Err>
-    where
-        F1: FnMut(&Import<Expr<E2>>) -> Result<E2, Err>,
-    {
-        match self {
-            ExprF::BinOp(BinOp::ImportAlt, l, r) => l
-                .as_ref()
-                .traverse_resolve_with_visitor(visitor)
-                .or_else(|_| r.as_ref().traverse_resolve_with_visitor(visitor)),
-            _ => {
-                let e = self.visit(&mut *visitor)?;
-                Ok(match &e {
-                    ExprF::Import(import) => ExprF::Embed((visitor.0)(import)?),
-                    _ => e,
-                })
-            }
-        }
+    pub fn map_mut<'a>(&'a mut self, mut map_subexpr: impl FnMut(&'a mut SE)) {
+        trivial_result(self.traverse_mut(|x| Ok(map_subexpr(x))))
     }
 }
 
@@ -349,6 +321,9 @@ impl<E> Expr<E> {
     pub fn as_ref(&self) -> &RawExpr<E> {
         &self.0.as_ref().0
     }
+    pub fn as_mut(&mut self) -> &mut RawExpr<E> {
+        &mut self.0.as_mut().0
+    }
 
     pub fn new(x: RawExpr<E>, n: Span) -> Self {
         Expr(Box::new((x, Some(n))))
@@ -365,14 +340,42 @@ impl<E> Expr<E> {
     pub fn rewrap<E2>(&self, x: RawExpr<E2>) -> Expr<E2> {
         Expr(Box::new((x, (self.0).1.clone())))
     }
-}
 
-impl<E> Expr<E> {
-    pub fn traverse_resolve<E2, Err>(
-        &self,
-        visit_import: impl FnMut(&Import<Expr<E2>>) -> Result<E2, Err>,
-    ) -> Result<Expr<E2>, Err> {
-        Ok(self.rewrap(self.as_ref().traverse_resolve(visit_import)?))
+    pub fn traverse_resolve_mut<Err, F1>(
+        &mut self,
+        f: &mut F1,
+    ) -> Result<(), Err>
+    where
+        E: Clone,
+        F1: FnMut(Import<Expr<E>>) -> Result<E, Err>,
+    {
+        match self.as_mut() {
+            ExprF::BinOp(BinOp::ImportAlt, l, r) => {
+                let garbage_expr = ExprF::BoolLit(false);
+                let new_self = if l.traverse_resolve_mut(f).is_ok() {
+                    l
+                } else {
+                    r.traverse_resolve_mut(f)?;
+                    r
+                };
+                *self.as_mut() =
+                    std::mem::replace(new_self.as_mut(), garbage_expr);
+            }
+            _ => {
+                self.as_mut().traverse_mut(|e| e.traverse_resolve_mut(f))?;
+                if let ExprF::Import(import) = self.as_mut() {
+                    let garbage_import = Import {
+                        mode: ImportMode::Code,
+                        location: ImportLocation::Missing,
+                        hash: None,
+                    };
+                    // Move out of &mut import
+                    let import = std::mem::replace(import, garbage_import);
+                    *self.as_mut() = ExprF::Embed(f(import)?);
+                }
+            }
+        }
+        Ok(())
     }
 }
 
diff --git a/dhall_syntax/src/core/import.rs b/dhall_syntax/src/core/import.rs
index cc38bb0..da3e99b 100644
--- a/dhall_syntax/src/core/import.rs
+++ b/dhall_syntax/src/core/import.rs
@@ -62,7 +62,7 @@ pub struct Import<SubExpr> {
 }
 
 impl<SE> URL<SE> {
-    pub fn visit_subexpr<'a, Err, SE2>(
+    pub fn traverse_ref<'a, Err, SE2>(
         &'a self,
         f: impl FnOnce(&'a SE) -> Result<SE2, Err>,
     ) -> Result<URL<SE2>, Err> {
@@ -75,32 +75,56 @@ impl<SE> URL<SE> {
             headers,
         })
     }
+    pub fn traverse_mut<'a, Err>(
+        &'a mut self,
+        f: impl FnOnce(&'a mut SE) -> Result<(), Err>,
+    ) -> Result<(), Err> {
+        if let Some(header) = &mut self.headers {
+            f(header)?;
+        }
+        Ok(())
+    }
 }
 
 impl<SE> ImportLocation<SE> {
-    pub fn visit_subexpr<'a, Err, SE2>(
+    pub fn traverse_ref<'a, Err, SE2>(
         &'a self,
         f: impl FnOnce(&'a SE) -> Result<SE2, Err>,
     ) -> Result<ImportLocation<SE2>, Err> {
         use ImportLocation::*;
         Ok(match self {
             Local(prefix, path) => Local(*prefix, path.clone()),
-            Remote(url) => Remote(url.visit_subexpr(f)?),
+            Remote(url) => Remote(url.traverse_ref(f)?),
             Env(env) => Env(env.clone()),
             Missing => Missing,
         })
     }
+    pub fn traverse_mut<'a, Err>(
+        &'a mut self,
+        f: impl FnOnce(&'a mut SE) -> Result<(), Err>,
+    ) -> Result<(), Err> {
+        if let ImportLocation::Remote(url) = self {
+            url.traverse_mut(f)?;
+        }
+        Ok(())
+    }
 }
 
 impl<SE> Import<SE> {
-    pub fn visit_subexpr<'a, Err, SE2>(
+    pub fn traverse_ref<'a, Err, SE2>(
         &'a self,
         f: impl FnOnce(&'a SE) -> Result<SE2, Err>,
     ) -> Result<Import<SE2>, Err> {
         Ok(Import {
             mode: self.mode,
-            location: self.location.visit_subexpr(f)?,
+            location: self.location.traverse_ref(f)?,
             hash: self.hash.clone(),
         })
     }
+    pub fn traverse_mut<'a, Err>(
+        &'a mut self,
+        f: impl FnOnce(&'a mut SE) -> Result<(), Err>,
+    ) -> Result<(), Err> {
+        self.location.traverse_mut(f)
+    }
 }
diff --git a/dhall_syntax/src/core/map.rs b/dhall_syntax/src/core/map.rs
index 6a0ebda..c4c6126 100644
--- a/dhall_syntax/src/core/map.rs
+++ b/dhall_syntax/src/core/map.rs
@@ -13,6 +13,8 @@ mod one_or_more {
     }
 
     pub type Iter<'a, T> = Either<slice::Iter<'a, T>, iter::Once<&'a T>>;
+    pub type IterMut<'a, T> =
+        Either<slice::IterMut<'a, T>, iter::Once<&'a mut T>>;
     pub type IntoIter<T> = Either<vec::IntoIter<T>, iter::Once<T>>;
 
     impl<T> OneOrMore<T> {
@@ -36,6 +38,13 @@ mod one_or_more {
                 OneOrMore::One(x) => Either::Right(iter::once(x)),
             }
         }
+
+        pub fn iter_mut(&mut self) -> IterMut<'_, T> {
+            match self {
+                OneOrMore::More(vec) => Either::Left(vec.iter_mut()),
+                OneOrMore::One(x) => Either::Right(iter::once(x)),
+            }
+        }
     }
 
     impl<T> IntoIterator for OneOrMore<T> {
@@ -76,6 +85,19 @@ mod dup_tree_map {
         iter: IterInternal<'a, K, V>,
         size: usize,
     }
+    pub type IterMutInternalIntermediate<'a, K, V> =
+        iter::Zip<iter::Repeat<&'a K>, one_or_more::IterMut<'a, V>>;
+    pub type IterMutInternal<'a, K, V> = iter::FlatMap<
+        btree_map::IterMut<'a, K, OneOrMore<V>>,
+        IterMutInternalIntermediate<'a, K, V>,
+        for<'b> fn(
+            (&'b K, &'b mut OneOrMore<V>),
+        ) -> IterMutInternalIntermediate<'b, K, V>,
+    >;
+    pub struct IterMut<'a, K, V> {
+        iter: IterMutInternal<'a, K, V>,
+        size: usize,
+    }
     pub type IntoIterInternalIntermediate<K, V> =
         iter::Zip<iter::Repeat<K>, one_or_more::IntoIter<V>>;
     pub type IntoIterInternal<K, V> = iter::FlatMap<
@@ -134,6 +156,21 @@ mod dup_tree_map {
                 size: self.size,
             }
         }
+
+        pub fn iter_mut(&mut self) -> IterMut<'_, K, V>
+        where
+            K: Ord,
+        {
+            fn foo<'a, K, V>(
+                (k, oom): (&'a K, &'a mut OneOrMore<V>),
+            ) -> IterMutInternalIntermediate<'a, K, V> {
+                iter::repeat(k).zip(oom.iter_mut())
+            }
+            IterMut {
+                iter: self.map.iter_mut().flat_map(foo),
+                size: self.size,
+            }
+        }
     }
 
     impl<K, V> Default for DupTreeMap<K, V>
@@ -180,6 +217,18 @@ mod dup_tree_map {
         }
     }
 
+    impl<'a, K, V> IntoIterator for &'a mut DupTreeMap<K, V>
+    where
+        K: Ord,
+    {
+        type Item = (&'a K, &'a mut V);
+        type IntoIter = IterMut<'a, K, V>;
+
+        fn into_iter(self) -> Self::IntoIter {
+            self.iter_mut()
+        }
+    }
+
     impl<K, V> iter::FromIterator<(K, V)> for DupTreeMap<K, V>
     where
         K: Ord,
@@ -212,6 +261,22 @@ mod dup_tree_map {
         }
     }
 
+    impl<'a, K, V> Iterator for IterMut<'a, K, V> {
+        type Item = (&'a K, &'a mut V);
+
+        fn next(&mut self) -> Option<Self::Item> {
+            let next = self.iter.next();
+            if next.is_some() {
+                self.size -= 1;
+            }
+            next
+        }
+
+        fn size_hint(&self) -> (usize, Option<usize>) {
+            (self.size, Some(self.size))
+        }
+    }
+
     impl<K, V> Iterator for IntoIter<K, V>
     where
         K: Clone,
diff --git a/dhall_syntax/src/core/text.rs b/dhall_syntax/src/core/text.rs
index 10fd68a..fb390ee 100644
--- a/dhall_syntax/src/core/text.rs
+++ b/dhall_syntax/src/core/text.rs
@@ -40,6 +40,52 @@ impl<SubExpr> InterpolatedTextContents<SubExpr> {
             Text(s) => s.is_empty(),
         }
     }
+
+    pub fn traverse_ref<'a, SubExpr2, E, F>(
+        &'a self,
+        mut f: F,
+    ) -> Result<InterpolatedTextContents<SubExpr2>, E>
+    where
+        F: FnMut(&'a SubExpr) -> Result<SubExpr2, E>,
+    {
+        use InterpolatedTextContents::{Expr, Text};
+        Ok(match self {
+            Expr(e) => Expr(f(e)?),
+            Text(s) => Text(s.clone()),
+        })
+    }
+    pub fn traverse_mut<'a, E, F>(&'a mut self, mut f: F) -> Result<(), E>
+    where
+        F: FnMut(&'a mut SubExpr) -> Result<(), E>,
+    {
+        use InterpolatedTextContents::Expr;
+        if let Expr(e) = self {
+            f(e)?;
+        }
+        Ok(())
+    }
+    pub fn map_ref<'a, SubExpr2, F>(
+        &'a self,
+        mut f: F,
+    ) -> InterpolatedTextContents<SubExpr2>
+    where
+        F: FnMut(&'a SubExpr) -> SubExpr2,
+    {
+        use InterpolatedTextContents::{Expr, Text};
+        match self {
+            Expr(e) => Expr(f(e)),
+            Text(s) => Text(s.clone()),
+        }
+    }
+    pub fn map_mut<'a, F>(&'a mut self, mut f: F)
+    where
+        F: FnMut(&'a mut SubExpr),
+    {
+        use InterpolatedTextContents::Expr;
+        if let Expr(e) = self {
+            f(e);
+        }
+    }
 }
 
 impl<SubExpr> InterpolatedText<SubExpr> {
@@ -76,6 +122,16 @@ impl<SubExpr> InterpolatedText<SubExpr> {
         })
     }
 
+    pub fn traverse_mut<'a, E, F>(&'a mut self, mut f: F) -> Result<(), E>
+    where
+        F: FnMut(&'a mut SubExpr) -> Result<(), E>,
+    {
+        for (e, _) in &mut self.tail {
+            f(e)?
+        }
+        Ok(())
+    }
+
     pub fn iter<'a>(
         &'a self,
     ) -> impl Iterator<Item = InterpolatedTextContents<&'a SubExpr>> + 'a {
diff --git a/dhall_syntax/src/core/visitor.rs b/dhall_syntax/src/core/visitor.rs
index 435771e..39a027f 100644
--- a/dhall_syntax/src/core/visitor.rs
+++ b/dhall_syntax/src/core/visitor.rs
@@ -1,11 +1,6 @@
 use crate::*;
 use std::iter::FromIterator;
 
-/// A way too generic Visitor trait.
-pub trait GenericVisitor<Input, Output>: Sized {
-    fn visit(self, input: Input) -> Output;
-}
-
 /// A visitor trait that can be used to traverse `ExprF`s. We need this pattern so that Rust lets
 /// us have as much mutability as we can.
 /// For example, `traverse_ref_with_special_handling_of_binders` cannot be made using only
@@ -14,7 +9,7 @@ pub trait GenericVisitor<Input, Output>: Sized {
 /// preventing exactly this ! So we have to be more clever. The visitor pattern allows us to have
 /// only one mutable thing the whole time: the visitor itself. The visitor can then carry around
 /// multiple closures or just one, and Rust is ok with either. See for example TraverseRefVisitor.
-pub trait ExprFFallibleVisitor<'a, SE1, SE2, E1, E2>: Sized {
+pub trait ExprFVisitor<'a, SE1, SE2, E1, E2>: Sized {
     type Error;
 
     fn visit_subexpr(&mut self, subexpr: &'a SE1) -> Result<SE2, Self::Error>;
@@ -27,174 +22,263 @@ pub trait ExprFFallibleVisitor<'a, SE1, SE2, E1, E2>: Sized {
     ) -> Result<SE2, Self::Error> {
         self.visit_subexpr(subexpr)
     }
+
+    fn visit(
+        self,
+        input: &'a ExprF<SE1, E1>,
+    ) -> Result<ExprF<SE2, E2>, Self::Error> {
+        visit_ref(self, input)
+    }
 }
 
-/// Like ExprFFallibleVisitor, but without the error handling.
-pub trait ExprFInFallibleVisitor<'a, SE1, SE2, E1, E2>: Sized {
-    fn visit_subexpr(&mut self, subexpr: &'a SE1) -> SE2;
-    fn visit_embed(self, embed: &'a E1) -> E2;
+/// Like `ExprFVisitor`, but by mutable reference
+pub trait ExprFMutVisitor<'a, SE, E>: Sized {
+    type Error;
+
+    fn visit_subexpr(&mut self, subexpr: &'a mut SE)
+        -> Result<(), Self::Error>;
+    fn visit_embed(self, _embed: &'a mut E) -> Result<(), Self::Error> {
+        Ok(())
+    }
 
     fn visit_subexpr_under_binder(
         mut self,
-        _label: &'a Label,
-        subexpr: &'a SE1,
-    ) -> SE2 {
+        _label: &'a mut Label,
+        subexpr: &'a mut SE,
+    ) -> Result<(), Self::Error> {
         self.visit_subexpr(subexpr)
     }
+
+    fn visit(self, input: &'a mut ExprF<SE, E>) -> Result<(), Self::Error> {
+        visit_mut(self, input)
+    }
 }
 
-impl<'a, T, SE1, SE2, E1, E2>
-    GenericVisitor<&'a ExprF<SE1, E1>, Result<ExprF<SE2, E2>, T::Error>> for T
+fn visit_ref<'a, V, SE1, SE2, E1, E2>(
+    mut v: V,
+    input: &'a ExprF<SE1, E1>,
+) -> Result<ExprF<SE2, E2>, V::Error>
 where
-    T: ExprFFallibleVisitor<'a, SE1, SE2, E1, E2>,
+    V: ExprFVisitor<'a, SE1, SE2, E1, E2>,
 {
-    fn visit(
-        self,
-        input: &'a ExprF<SE1, E1>,
-    ) -> Result<ExprF<SE2, E2>, T::Error> {
-        fn vec<'a, T, U, Err, F: FnMut(&'a T) -> Result<U, Err>>(
-            x: &'a [T],
-            f: F,
-        ) -> Result<Vec<U>, Err> {
-            x.iter().map(f).collect()
-        }
-        fn opt<'a, T, U, Err, F: FnOnce(&'a T) -> Result<U, Err>>(
-            x: &'a Option<T>,
-            f: F,
-        ) -> Result<Option<U>, Err> {
-            Ok(match x {
-                Some(x) => Some(f(x)?),
-                None => None,
+    fn vec<'a, T, U, Err, F: FnMut(&'a T) -> Result<U, Err>>(
+        x: &'a [T],
+        f: F,
+    ) -> Result<Vec<U>, Err> {
+        x.iter().map(f).collect()
+    }
+    fn opt<'a, T, U, Err, F: FnOnce(&'a T) -> Result<U, Err>>(
+        x: &'a Option<T>,
+        f: F,
+    ) -> Result<Option<U>, Err> {
+        Ok(match x {
+            Some(x) => Some(f(x)?),
+            None => None,
+        })
+    }
+    fn dupmap<'a, V, SE1, SE2, E1, E2, T>(
+        x: impl IntoIterator<Item = (&'a Label, &'a SE1)>,
+        mut v: V,
+    ) -> Result<T, V::Error>
+    where
+        SE1: 'a,
+        T: FromIterator<(Label, SE2)>,
+        V: ExprFVisitor<'a, SE1, SE2, E1, E2>,
+    {
+        x.into_iter()
+            .map(|(k, x)| Ok((k.clone(), v.visit_subexpr(x)?)))
+            .collect()
+    }
+    fn optdupmap<'a, V, SE1, SE2, E1, E2, T>(
+        x: impl IntoIterator<Item = (&'a Label, &'a Option<SE1>)>,
+        mut v: V,
+    ) -> Result<T, V::Error>
+    where
+        SE1: 'a,
+        T: FromIterator<(Label, Option<SE2>)>,
+        V: ExprFVisitor<'a, SE1, SE2, E1, E2>,
+    {
+        x.into_iter()
+            .map(|(k, x)| {
+                Ok((
+                    k.clone(),
+                    match x {
+                        Some(x) => Some(v.visit_subexpr(x)?),
+                        None => None,
+                    },
+                ))
             })
+            .collect()
+    }
+
+    use crate::ExprF::*;
+    Ok(match input {
+        Var(v) => Var(v.clone()),
+        Lam(l, t, e) => {
+            let t = v.visit_subexpr(t)?;
+            let e = v.visit_subexpr_under_binder(l, e)?;
+            Lam(l.clone(), t, e)
         }
-        fn dupmap<'a, V, SE1, SE2, E1, E2, T>(
-            x: impl IntoIterator<Item = (&'a Label, &'a SE1)>,
-            mut v: V,
-        ) -> Result<T, V::Error>
-        where
-            SE1: 'a,
-            T: FromIterator<(Label, SE2)>,
-            V: ExprFFallibleVisitor<'a, SE1, SE2, E1, E2>,
-        {
-            x.into_iter()
-                .map(|(k, x)| Ok((k.clone(), v.visit_subexpr(x)?)))
-                .collect()
+        Pi(l, t, e) => {
+            let t = v.visit_subexpr(t)?;
+            let e = v.visit_subexpr_under_binder(l, e)?;
+            Pi(l.clone(), t, e)
         }
-        fn optdupmap<'a, V, SE1, SE2, E1, E2, T>(
-            x: impl IntoIterator<Item = (&'a Label, &'a Option<SE1>)>,
-            mut v: V,
-        ) -> Result<T, V::Error>
-        where
-            SE1: 'a,
-            T: FromIterator<(Label, Option<SE2>)>,
-            V: ExprFFallibleVisitor<'a, SE1, SE2, E1, E2>,
-        {
-            x.into_iter()
-                .map(|(k, x)| {
-                    Ok((
-                        k.clone(),
-                        match x {
-                            Some(x) => Some(v.visit_subexpr(x)?),
-                            None => None,
-                        },
-                    ))
-                })
-                .collect()
+        Let(l, t, a, e) => {
+            let t = opt(t, &mut |e| v.visit_subexpr(e))?;
+            let a = v.visit_subexpr(a)?;
+            let e = v.visit_subexpr_under_binder(l, e)?;
+            Let(l.clone(), t, a, e)
         }
-
-        let mut v = self;
-        use crate::ExprF::*;
-        Ok(match input {
-            Var(v) => Var(v.clone()),
-            Lam(l, t, e) => {
-                let t = v.visit_subexpr(t)?;
-                let e = v.visit_subexpr_under_binder(l, e)?;
-                Lam(l.clone(), t, e)
-            }
-            Pi(l, t, e) => {
-                let t = v.visit_subexpr(t)?;
-                let e = v.visit_subexpr_under_binder(l, e)?;
-                Pi(l.clone(), t, e)
-            }
-            Let(l, t, a, e) => {
-                let t = opt(t, &mut |e| v.visit_subexpr(e))?;
-                let a = v.visit_subexpr(a)?;
-                let e = v.visit_subexpr_under_binder(l, e)?;
-                Let(l.clone(), t, a, e)
-            }
-            App(f, a) => App(v.visit_subexpr(f)?, v.visit_subexpr(a)?),
-            Annot(x, t) => Annot(v.visit_subexpr(x)?, v.visit_subexpr(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.traverse_ref(|e| v.visit_subexpr(e))?),
-            BinOp(o, x, y) => {
-                BinOp(*o, v.visit_subexpr(x)?, v.visit_subexpr(y)?)
-            }
-            BoolIf(b, t, f) => BoolIf(
-                v.visit_subexpr(b)?,
-                v.visit_subexpr(t)?,
-                v.visit_subexpr(f)?,
-            ),
-            EmptyListLit(t) => EmptyListLit(v.visit_subexpr(t)?),
-            NEListLit(es) => NEListLit(vec(es, |e| v.visit_subexpr(e))?),
-            SomeLit(e) => SomeLit(v.visit_subexpr(e)?),
-            RecordType(kts) => RecordType(dupmap(kts, v)?),
-            RecordLit(kvs) => RecordLit(dupmap(kvs, v)?),
-            UnionType(kts) => UnionType(optdupmap(kts, v)?),
-            Merge(x, y, t) => Merge(
-                v.visit_subexpr(x)?,
-                v.visit_subexpr(y)?,
-                opt(t, |e| v.visit_subexpr(e))?,
-            ),
-            ToMap(x, t) => {
-                ToMap(v.visit_subexpr(x)?, opt(t, |e| v.visit_subexpr(e))?)
-            }
-            Field(e, l) => Field(v.visit_subexpr(e)?, l.clone()),
-            Projection(e, ls) => Projection(v.visit_subexpr(e)?, ls.clone()),
-            Assert(e) => Assert(v.visit_subexpr(e)?),
-            Import(i) => Import(i.visit_subexpr(|e| v.visit_subexpr(e))?),
-            Embed(a) => Embed(v.visit_embed(a)?),
-        })
-    }
+        App(f, a) => App(v.visit_subexpr(f)?, v.visit_subexpr(a)?),
+        Annot(x, t) => Annot(v.visit_subexpr(x)?, v.visit_subexpr(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.traverse_ref(|e| v.visit_subexpr(e))?),
+        BinOp(o, x, y) => BinOp(*o, v.visit_subexpr(x)?, v.visit_subexpr(y)?),
+        BoolIf(b, t, f) => BoolIf(
+            v.visit_subexpr(b)?,
+            v.visit_subexpr(t)?,
+            v.visit_subexpr(f)?,
+        ),
+        EmptyListLit(t) => EmptyListLit(v.visit_subexpr(t)?),
+        NEListLit(es) => NEListLit(vec(es, |e| v.visit_subexpr(e))?),
+        SomeLit(e) => SomeLit(v.visit_subexpr(e)?),
+        RecordType(kts) => RecordType(dupmap(kts, v)?),
+        RecordLit(kvs) => RecordLit(dupmap(kvs, v)?),
+        UnionType(kts) => UnionType(optdupmap(kts, v)?),
+        Merge(x, y, t) => Merge(
+            v.visit_subexpr(x)?,
+            v.visit_subexpr(y)?,
+            opt(t, |e| v.visit_subexpr(e))?,
+        ),
+        ToMap(x, t) => {
+            ToMap(v.visit_subexpr(x)?, opt(t, |e| v.visit_subexpr(e))?)
+        }
+        Field(e, l) => Field(v.visit_subexpr(e)?, l.clone()),
+        Projection(e, ls) => Projection(v.visit_subexpr(e)?, ls.clone()),
+        Assert(e) => Assert(v.visit_subexpr(e)?),
+        Import(i) => Import(i.traverse_ref(|e| v.visit_subexpr(e))?),
+        Embed(a) => Embed(v.visit_embed(a)?),
+    })
 }
 
-impl<'a, T, SE1, SE2, E1, E2> GenericVisitor<&'a ExprF<SE1, E1>, ExprF<SE2, E2>>
-    for T
+fn visit_mut<'a, V, SE, E>(
+    mut v: V,
+    input: &'a mut ExprF<SE, E>,
+) -> Result<(), V::Error>
 where
-    T: ExprFInFallibleVisitor<'a, SE1, SE2, E1, E2>,
+    V: ExprFMutVisitor<'a, SE, E>,
 {
-    fn visit(self, input: &'a ExprF<SE1, E1>) -> ExprF<SE2, E2> {
-        trivial_result(InfallibleWrapper(self).visit(input))
+    fn vec<'a, V, SE, E>(v: &mut V, x: &'a mut Vec<SE>) -> Result<(), V::Error>
+    where
+        V: ExprFMutVisitor<'a, SE, E>,
+    {
+        for x in x {
+            v.visit_subexpr(x)?;
+        }
+        Ok(())
     }
-}
-
-struct InfallibleWrapper<T>(T);
-
-impl<'a, T, SE1, SE2, E1, E2> ExprFFallibleVisitor<'a, SE1, SE2, E1, E2>
-    for InfallibleWrapper<T>
-where
-    T: ExprFInFallibleVisitor<'a, SE1, SE2, E1, E2>,
-{
-    type Error = !;
-
-    fn visit_subexpr(&mut self, subexpr: &'a SE1) -> Result<SE2, Self::Error> {
-        Ok(self.0.visit_subexpr(subexpr))
+    fn opt<'a, V, SE, E>(
+        v: &mut V,
+        x: &'a mut Option<SE>,
+    ) -> Result<(), V::Error>
+    where
+        V: ExprFMutVisitor<'a, SE, E>,
+    {
+        if let Some(x) = x {
+            v.visit_subexpr(x)?;
+        }
+        Ok(())
     }
-    fn visit_embed(self, embed: &'a E1) -> Result<E2, Self::Error> {
-        Ok(self.0.visit_embed(embed))
+    fn dupmap<'a, V, SE, E>(
+        mut v: V,
+        x: impl IntoIterator<Item = (&'a Label, &'a mut SE)>,
+    ) -> Result<(), V::Error>
+    where
+        SE: 'a,
+        V: ExprFMutVisitor<'a, SE, E>,
+    {
+        for (_, x) in x {
+            v.visit_subexpr(x)?;
+        }
+        Ok(())
+    }
+    fn optdupmap<'a, V, SE, E>(
+        mut v: V,
+        x: impl IntoIterator<Item = (&'a Label, &'a mut Option<SE>)>,
+    ) -> Result<(), V::Error>
+    where
+        SE: 'a,
+        V: ExprFMutVisitor<'a, SE, E>,
+    {
+        for (_, x) in x {
+            opt(&mut v, x)?;
+        }
+        Ok(())
     }
 
-    fn visit_subexpr_under_binder(
-        self,
-        label: &'a Label,
-        subexpr: &'a SE1,
-    ) -> Result<SE2, Self::Error> {
-        Ok(self.0.visit_subexpr_under_binder(label, subexpr))
+    use crate::ExprF::*;
+    match input {
+        Var(_) | Const(_) | Builtin(_) | BoolLit(_) | NaturalLit(_)
+        | IntegerLit(_) | DoubleLit(_) => {}
+        Lam(l, t, e) => {
+            v.visit_subexpr(t)?;
+            v.visit_subexpr_under_binder(l, e)?;
+        }
+        Pi(l, t, e) => {
+            v.visit_subexpr(t)?;
+            v.visit_subexpr_under_binder(l, e)?;
+        }
+        Let(l, t, a, e) => {
+            opt(&mut v, t)?;
+            v.visit_subexpr(a)?;
+            v.visit_subexpr_under_binder(l, e)?;
+        }
+        App(f, a) => {
+            v.visit_subexpr(f)?;
+            v.visit_subexpr(a)?;
+        }
+        Annot(x, t) => {
+            v.visit_subexpr(x)?;
+            v.visit_subexpr(t)?;
+        }
+        TextLit(t) => t.traverse_mut(|e| v.visit_subexpr(e))?,
+        BinOp(_, x, y) => {
+            v.visit_subexpr(x)?;
+            v.visit_subexpr(y)?;
+        }
+        BoolIf(b, t, f) => {
+            v.visit_subexpr(b)?;
+            v.visit_subexpr(t)?;
+            v.visit_subexpr(f)?;
+        }
+        EmptyListLit(t) => v.visit_subexpr(t)?,
+        NEListLit(es) => vec(&mut v, es)?,
+        SomeLit(e) => v.visit_subexpr(e)?,
+        RecordType(kts) => dupmap(v, kts)?,
+        RecordLit(kvs) => dupmap(v, kvs)?,
+        UnionType(kts) => optdupmap(v, kts)?,
+        Merge(x, y, t) => {
+            v.visit_subexpr(x)?;
+            v.visit_subexpr(y)?;
+            opt(&mut v, t)?;
+        }
+        ToMap(x, t) => {
+            v.visit_subexpr(x)?;
+            opt(&mut v, t)?;
+        }
+        Field(e, _) => v.visit_subexpr(e)?,
+        Projection(e, _) => v.visit_subexpr(e)?,
+        Assert(e) => v.visit_subexpr(e)?,
+        Import(i) => i.traverse_mut(|e| v.visit_subexpr(e))?,
+        Embed(a) => v.visit_embed(a)?,
     }
+    Ok(())
 }
 
 pub struct TraverseRefWithBindersVisitor<F1, F2> {
@@ -202,7 +286,7 @@ pub struct TraverseRefWithBindersVisitor<F1, F2> {
     pub visit_under_binder: F2,
 }
 
-impl<'a, SE, E, SE2, Err, F1, F2> ExprFFallibleVisitor<'a, SE, SE2, E, E>
+impl<'a, SE, E, SE2, Err, F1, F2> ExprFVisitor<'a, SE, SE2, E, E>
     for TraverseRefWithBindersVisitor<F1, F2>
 where
     SE: 'a,
@@ -231,7 +315,7 @@ pub struct TraverseRefVisitor<F1> {
     pub visit_subexpr: F1,
 }
 
-impl<'a, SE, E, SE2, Err, F1> ExprFFallibleVisitor<'a, SE, SE2, E, E>
+impl<'a, SE, E, SE2, Err, F1> ExprFVisitor<'a, SE, SE2, E, E>
     for TraverseRefVisitor<F1>
 where
     SE: 'a,
@@ -248,26 +332,22 @@ where
     }
 }
 
-pub struct ResolveVisitor<F1>(pub F1);
+pub struct TraverseMutVisitor<F1> {
+    pub visit_subexpr: F1,
+}
 
-impl<'a, 'b, E, E2, Err, F1> ExprFFallibleVisitor<'a, Expr<E>, Expr<E2>, E, E2>
-    for &'b mut ResolveVisitor<F1>
+impl<'a, SE, E, Err, F1> ExprFMutVisitor<'a, SE, E> for TraverseMutVisitor<F1>
 where
-    F1: FnMut(&Import<Expr<E2>>) -> Result<E2, Err>,
+    SE: 'a,
+    E: 'a,
+    F1: FnMut(&'a mut SE) -> Result<(), Err>,
 {
     type Error = Err;
 
     fn visit_subexpr(
         &mut self,
-        subexpr: &'a Expr<E>,
-    ) -> Result<Expr<E2>, Self::Error> {
-        Ok(subexpr.rewrap(
-            subexpr
-                .as_ref()
-                .traverse_resolve_with_visitor(&mut **self)?,
-        ))
-    }
-    fn visit_embed(self, _embed: &'a E) -> Result<E2, Self::Error> {
-        unimplemented!()
+        subexpr: &'a mut SE,
+    ) -> Result<(), Self::Error> {
+        (self.visit_subexpr)(subexpr)
     }
 }
diff --git a/dhall_syntax/src/parser.rs b/dhall_syntax/src/parser.rs
index 1262774..41d6d04 100644
--- a/dhall_syntax/src/parser.rs
+++ b/dhall_syntax/src/parser.rs
@@ -60,17 +60,32 @@ impl<'input> ParseInput<'input, Rule> {
             original_input_str: self.original_input_str.clone(),
         }
     }
+    /// If the contained pair has exactly one child, return a new Self containing it.
+    fn single_child(&self) -> Option<Self> {
+        let mut children = self.pair.clone().into_inner();
+        if let Some(child) = children.next() {
+            if children.next().is_none() {
+                return Some(self.with_pair(child));
+            }
+        }
+        None
+    }
     fn as_span(&self) -> Span {
         Span::make(self.original_input_str.clone(), self.pair.as_span())
     }
     fn as_str(&self) -> &'input str {
         self.pair.as_str()
     }
+    fn as_rule(&self) -> Rule {
+        self.pair.as_rule()
+    }
 }
 
-// Used to retrieve the `Rule` enum associated with the `Self` type in `parse_children`.
+// Used by the macros.
 trait PestConsumer {
-    type RuleEnum: pest::RuleType;
+    type Rule: pest::RuleType;
+    fn rule_alias(rule: Self::Rule) -> String;
+    fn allows_shortcut(rule: Self::Rule) -> bool;
 }
 
 fn debug_pair(pair: Pair<Rule>) -> String {
@@ -231,21 +246,17 @@ struct Parsers;
 
 #[make_parser(Rule)]
 impl Parsers {
-    fn EOI(_: ParseInput<Rule>) -> ParseResult<()> {
+    fn EOI(_input: ParseInput<Rule>) -> ParseResult<()> {
         Ok(())
     }
 
+    #[alias(label)]
     fn simple_label(input: ParseInput<Rule>) -> ParseResult<Label> {
-        Ok(Label::from(input.as_str().trim().to_owned()))
+        Ok(Label::from(input.as_str()))
     }
+    #[alias(label)]
     fn quoted_label(input: ParseInput<Rule>) -> ParseResult<Label> {
-        Ok(Label::from(input.as_str().trim().to_owned()))
-    }
-    fn label(input: ParseInput<Rule>) -> ParseResult<Label> {
-        Ok(parse_children!(input;
-            [simple_label(l)] => l,
-            [quoted_label(l)] => l,
-        ))
+        Ok(Label::from(input.as_str()))
     }
 
     fn double_quote_literal<E: Clone>(
@@ -262,17 +273,15 @@ impl Parsers {
         input: ParseInput<Rule>,
     ) -> ParseResult<ParsedTextContents<E>> {
         Ok(parse_children!(input;
-            [interpolation(e)] => {
+            [expression(e)] => {
                 InterpolatedTextContents::Expr(e)
             },
-            [double_quote_escaped(s)] => {
-                InterpolatedTextContents::Text(s)
-            },
             [double_quote_char(s)] => {
-                InterpolatedTextContents::Text(s.to_owned())
+                InterpolatedTextContents::Text(s)
             },
         ))
     }
+    #[alias(double_quote_char)]
     fn double_quote_escaped(input: ParseInput<Rule>) -> ParseResult<String> {
         Ok(match input.as_str() {
             "\"" => "\"".to_owned(),
@@ -345,8 +354,8 @@ impl Parsers {
     }
     fn double_quote_char<'a>(
         input: ParseInput<'a, Rule>,
-    ) -> ParseResult<&'a str> {
-        Ok(input.as_str())
+    ) -> ParseResult<String> {
+        Ok(input.as_str().to_owned())
     }
 
     fn single_quote_literal<E: Clone>(
@@ -356,6 +365,7 @@ impl Parsers {
             [single_quote_continue(lines)] => {
                 let newline: ParsedText<E> = "\n".to_string().into();
 
+                // Reverse lines and chars in each line
                 let mut lines: Vec<ParsedText<E>> = lines
                     .into_iter()
                     .rev()
@@ -377,44 +387,27 @@ impl Parsers {
     ) -> ParseResult<&'a str> {
         Ok(input.as_str())
     }
-    fn escaped_quote_pair<'a>(_: ParseInput<'a, Rule>) -> ParseResult<&'a str> {
+    #[alias(single_quote_char)]
+    fn escaped_quote_pair<'a>(
+        _input: ParseInput<'a, Rule>,
+    ) -> ParseResult<&'a str> {
         Ok("''")
     }
+    #[alias(single_quote_char)]
     fn escaped_interpolation<'a>(
-        _: ParseInput<'a, Rule>,
+        _input: ParseInput<'a, Rule>,
     ) -> ParseResult<&'a str> {
         Ok("${")
     }
-    fn interpolation<E: Clone>(
-        input: ParseInput<Rule>,
-    ) -> ParseResult<Expr<E>> {
-        Ok(parse_children!(input;
-            [expression(e)] => e
-        ))
-    }
 
     // Returns a vec of lines in reversed order, where each line is also in reversed order.
     fn single_quote_continue<E: Clone>(
         input: ParseInput<Rule>,
     ) -> ParseResult<Vec<Vec<ParsedTextContents<E>>>> {
         Ok(parse_children!(input;
-            [interpolation(c), single_quote_continue(lines)] => {
-                let c = InterpolatedTextContents::Expr(c);
-                let mut lines = lines;
-                lines.last_mut().unwrap().push(c);
-                lines
-            },
-            [escaped_quote_pair(c), single_quote_continue(lines)] => {
+            [expression(e), single_quote_continue(lines)] => {
+                let c = InterpolatedTextContents::Expr(e);
                 let mut lines = lines;
-                // TODO: don't allocate for every char
-                let c = InterpolatedTextContents::Text(c.to_owned());
-                lines.last_mut().unwrap().push(c);
-                lines
-            },
-            [escaped_interpolation(c), single_quote_continue(lines)] => {
-                let mut lines = lines;
-                // TODO: don't allocate for every char
-                let c = InterpolatedTextContents::Text(c.to_owned());
                 lines.last_mut().unwrap().push(c);
                 lines
             },
@@ -435,38 +428,41 @@ impl Parsers {
         ))
     }
 
+    #[alias(expression)]
     fn builtin<E: Clone>(input: ParseInput<Rule>) -> ParseResult<Expr<E>> {
         let s = input.as_str();
-        let span = input.as_span();
-        Ok(spanned(
-            span,
-            match crate::Builtin::parse(s) {
-                Some(b) => Builtin(b),
-                None => {
-                    match s {
-                        "True" => BoolLit(true),
-                        "False" => BoolLit(false),
-                        "Type" => Const(crate::Const::Type),
-                        "Kind" => Const(crate::Const::Kind),
-                        "Sort" => Const(crate::Const::Sort),
-                        _ => Err(input
-                            .error(format!("Unrecognized builtin: '{}'", s)))?,
-                    }
-                }
+        let e = match crate::Builtin::parse(s) {
+            Some(b) => Builtin(b),
+            None => match s {
+                "True" => BoolLit(true),
+                "False" => BoolLit(false),
+                "Type" => Const(crate::Const::Type),
+                "Kind" => Const(crate::Const::Kind),
+                "Sort" => Const(crate::Const::Sort),
+                _ => Err(input.error(format!("Unrecognized builtin: '{}'", s)))?,
             },
-        ))
+        };
+        Ok(spanned(input.as_span(), e))
     }
 
-    fn NaN(_: ParseInput<Rule>) -> ParseResult<()> {
-        Ok(())
+    #[alias(double_literal)]
+    fn NaN(_input: ParseInput<Rule>) -> ParseResult<core::Double> {
+        Ok(std::f64::NAN.into())
     }
-    fn minus_infinity_literal(_: ParseInput<Rule>) -> ParseResult<()> {
-        Ok(())
+    #[alias(double_literal)]
+    fn minus_infinity_literal(
+        _input: ParseInput<Rule>,
+    ) -> ParseResult<core::Double> {
+        Ok(std::f64::NEG_INFINITY.into())
     }
-    fn plus_infinity_literal(_: ParseInput<Rule>) -> ParseResult<()> {
-        Ok(())
+    #[alias(double_literal)]
+    fn plus_infinity_literal(
+        _input: ParseInput<Rule>,
+    ) -> ParseResult<core::Double> {
+        Ok(std::f64::INFINITY.into())
     }
 
+    #[alias(double_literal)]
     fn numeric_double_literal(
         input: ParseInput<Rule>,
     ) -> ParseResult<core::Double> {
@@ -481,15 +477,6 @@ impl Parsers {
         }
     }
 
-    fn double_literal(input: ParseInput<Rule>) -> ParseResult<core::Double> {
-        Ok(parse_children!(input;
-            [numeric_double_literal(n)] => n,
-            [minus_infinity_literal(_)] => std::f64::NEG_INFINITY.into(),
-            [plus_infinity_literal(_)] => std::f64::INFINITY.into(),
-            [NaN(_)] => std::f64::NAN.into(),
-        ))
-    }
-
     fn natural_literal(input: ParseInput<Rule>) -> ParseResult<core::Natural> {
         input
             .as_str()
@@ -506,13 +493,13 @@ impl Parsers {
             .map_err(|e| input.error(format!("{}", e)))
     }
 
+    #[alias(expression, shortcut = true)]
     fn identifier<E: Clone>(input: ParseInput<Rule>) -> ParseResult<Expr<E>> {
-        let span = input.as_span();
         Ok(parse_children!(input;
             [variable(v)] => {
-                spanned(span, Var(v))
+                spanned(input.as_span(), Var(v))
             },
-            [builtin(e)] => e,
+            [expression(e)] => e,
         ))
     }
 
@@ -527,42 +514,40 @@ impl Parsers {
         ))
     }
 
+    #[alias(path_component)]
     fn unquoted_path_component<'a>(
         input: ParseInput<'a, Rule>,
-    ) -> ParseResult<&'a str> {
-        Ok(input.as_str())
+    ) -> ParseResult<String> {
+        Ok(input.as_str().to_string())
     }
+    #[alias(path_component)]
     fn quoted_path_component<'a>(
         input: ParseInput<'a, Rule>,
-    ) -> ParseResult<&'a str> {
-        Ok(input.as_str())
-    }
-    fn path_component(input: ParseInput<Rule>) -> ParseResult<String> {
-        Ok(parse_children!(input;
-            [unquoted_path_component(s)] => s.to_string(),
-            [quoted_path_component(s)] => {
-                const RESERVED: &percent_encoding::AsciiSet =
-                    &percent_encoding::CONTROLS
-                    .add(b'=').add(b':').add(b'/').add(b'?')
-                    .add(b'#').add(b'[').add(b']').add(b'@')
-                    .add(b'!').add(b'$').add(b'&').add(b'\'')
-                    .add(b'(').add(b')').add(b'*').add(b'+')
-                    .add(b',').add(b';');
-                s.chars()
-                    .map(|c| {
-                        // Percent-encode ascii chars
-                        if c.is_ascii() {
-                            percent_encoding::utf8_percent_encode(
-                                &c.to_string(),
-                                RESERVED,
-                            ).to_string()
-                        } else {
-                            c.to_string()
-                        }
-                    })
-                    .collect()
-            },
-        ))
+    ) -> ParseResult<String> {
+        #[rustfmt::skip]
+        const RESERVED: &percent_encoding::AsciiSet =
+            &percent_encoding::CONTROLS
+            .add(b'=').add(b':').add(b'/').add(b'?')
+            .add(b'#').add(b'[').add(b']').add(b'@')
+            .add(b'!').add(b'$').add(b'&').add(b'\'')
+            .add(b'(').add(b')').add(b'*').add(b'+')
+            .add(b',').add(b';');
+        Ok(input
+            .as_str()
+            .chars()
+            .map(|c| {
+                // Percent-encode ascii chars
+                if c.is_ascii() {
+                    percent_encoding::utf8_percent_encode(
+                        &c.to_string(),
+                        RESERVED,
+                    )
+                    .to_string()
+                } else {
+                    c.to_string()
+                }
+            })
+            .collect())
     }
     fn path(input: ParseInput<Rule>) -> ParseResult<FilePath> {
         Ok(parse_children!(input;
@@ -572,30 +557,40 @@ impl Parsers {
         ))
     }
 
-    fn local(input: ParseInput<Rule>) -> ParseResult<(FilePrefix, FilePath)> {
+    #[alias(import_type)]
+    fn local<E: Clone>(
+        input: ParseInput<Rule>,
+    ) -> ParseResult<ImportLocation<Expr<E>>> {
         Ok(parse_children!(input;
-            [parent_path(l)] => l,
-            [here_path(l)] => l,
-            [home_path(l)] => l,
-            [absolute_path(l)] => l,
+            [local_path((prefix, p))] => ImportLocation::Local(prefix, p),
         ))
     }
 
-    fn parent_path(input: ParseInput<Rule>) -> ParseResult<(FilePrefix, FilePath)> {
+    #[alias(local_path)]
+    fn parent_path(
+        input: ParseInput<Rule>,
+    ) -> ParseResult<(FilePrefix, FilePath)> {
         Ok(parse_children!(input;
             [path(p)] => (FilePrefix::Parent, p)
         ))
     }
-    fn here_path(input: ParseInput<Rule>) -> ParseResult<(FilePrefix, FilePath)> {
+    #[alias(local_path)]
+    fn here_path(
+        input: ParseInput<Rule>,
+    ) -> ParseResult<(FilePrefix, FilePath)> {
         Ok(parse_children!(input;
             [path(p)] => (FilePrefix::Here, p)
         ))
     }
-    fn home_path(input: ParseInput<Rule>) -> ParseResult<(FilePrefix, FilePath)> {
+    #[alias(local_path)]
+    fn home_path(
+        input: ParseInput<Rule>,
+    ) -> ParseResult<(FilePrefix, FilePath)> {
         Ok(parse_children!(input;
             [path(p)] => (FilePrefix::Home, p)
         ))
     }
+    #[alias(local_path)]
     fn absolute_path(
         input: ParseInput<Rule>,
     ) -> ParseResult<(FilePrefix, FilePath)> {
@@ -641,25 +636,31 @@ impl Parsers {
         Ok(input.as_str().to_owned())
     }
 
-    fn http<E: Clone>(input: ParseInput<Rule>) -> ParseResult<URL<Expr<E>>> {
-        Ok(parse_children!(input;
-        [http_raw(url)] => url,
-        [http_raw(url), import_expression(e)] =>
-            URL { headers: Some(e), ..url },
-        ))
+    #[alias(import_type)]
+    fn http<E: Clone>(
+        input: ParseInput<Rule>,
+    ) -> ParseResult<ImportLocation<Expr<E>>> {
+        Ok(ImportLocation::Remote(parse_children!(input;
+            [http_raw(url)] => url,
+            [http_raw(url), expression(e)] => URL { headers: Some(e), ..url },
+        )))
     }
 
-    fn env(input: ParseInput<Rule>) -> ParseResult<String> {
+    #[alias(import_type)]
+    fn env<E: Clone>(
+        input: ParseInput<Rule>,
+    ) -> ParseResult<ImportLocation<Expr<E>>> {
         Ok(parse_children!(input;
-            [bash_environment_variable(s)] => s,
-            [posix_environment_variable(s)] => s,
+            [environment_variable(v)] => ImportLocation::Env(v),
         ))
     }
+    #[alias(environment_variable)]
     fn bash_environment_variable(
         input: ParseInput<Rule>,
     ) -> ParseResult<String> {
         Ok(input.as_str().to_owned())
     }
+    #[alias(environment_variable)]
     fn posix_environment_variable(
         input: ParseInput<Rule>,
     ) -> ParseResult<String> {
@@ -686,27 +687,11 @@ impl Parsers {
         })
     }
 
-    fn missing(_: ParseInput<Rule>) -> ParseResult<()> {
-        Ok(())
-    }
-
-    fn import_type<E: Clone>(
-        input: ParseInput<Rule>,
+    #[alias(import_type)]
+    fn missing<E: Clone>(
+        _input: ParseInput<Rule>,
     ) -> ParseResult<ImportLocation<Expr<E>>> {
-        Ok(parse_children!(input;
-            [missing(_)] => {
-                ImportLocation::Missing
-            },
-            [env(e)] => {
-                ImportLocation::Env(e)
-            },
-            [http(url)] => {
-                ImportLocation::Remote(url)
-            },
-            [local((prefix, p))] => {
-                ImportLocation::Local(prefix, p)
-            },
-        ))
+        Ok(ImportLocation::Missing)
     }
 
     fn hash(input: ParseInput<Rule>) -> ParseResult<Hash> {
@@ -722,78 +707,65 @@ impl Parsers {
     fn import_hashed<E: Clone>(
         input: ParseInput<Rule>,
     ) -> ParseResult<crate::Import<Expr<E>>> {
+        use crate::Import;
+        let mode = ImportMode::Code;
         Ok(parse_children!(input;
-        [import_type(location)] =>
-            crate::Import {mode: ImportMode::Code, location, hash: None },
-        [import_type(location), hash(h)] =>
-        crate::Import {mode: ImportMode::Code, location, hash: Some(h) },
+            [import_type(location)] => Import { mode, location, hash: None },
+            [import_type(location), hash(h)] => Import { mode, location, hash: Some(h) },
         ))
     }
 
-    fn Text(_: ParseInput<Rule>) -> ParseResult<()> {
-        Ok(())
+    #[alias(import_mode)]
+    fn Text(_input: ParseInput<Rule>) -> ParseResult<ImportMode> {
+        Ok(ImportMode::RawText)
     }
-    fn Location(_: ParseInput<Rule>) -> ParseResult<()> {
-        Ok(())
+    #[alias(import_mode)]
+    fn Location(_input: ParseInput<Rule>) -> ParseResult<ImportMode> {
+        Ok(ImportMode::Location)
     }
 
+    #[alias(expression)]
     fn import<E: Clone>(input: ParseInput<Rule>) -> ParseResult<Expr<E>> {
-        let span = input.as_span();
-        Ok(parse_children!(input;
+        use crate::Import;
+        let import = parse_children!(input;
             [import_hashed(imp)] => {
-                spanned(span, Import(crate::Import {
-                    mode: ImportMode::Code,
-                    ..imp
-                }))
-            },
-            [import_hashed(imp), Text(_)] => {
-                spanned(span, Import(crate::Import {
-                    mode: ImportMode::RawText,
-                    ..imp
-                }))
+                Import { mode: ImportMode::Code, ..imp }
             },
-            [import_hashed(imp), Location(_)] => {
-                spanned(span, Import(crate::Import {
-                    mode: ImportMode::Location,
-                    ..imp
-                }))
+            [import_hashed(imp), import_mode(mode)] => {
+                Import { mode, ..imp }
             },
-        ))
+        );
+        Ok(spanned(input.as_span(), Import(import)))
     }
 
-    fn lambda(_: ParseInput<Rule>) -> ParseResult<()> {
-        Ok(())
-    }
-    fn forall(_: ParseInput<Rule>) -> ParseResult<()> {
+    fn lambda(_input: ParseInput<Rule>) -> ParseResult<()> {
         Ok(())
     }
-    fn arrow(_: ParseInput<Rule>) -> ParseResult<()> {
+    fn forall(_input: ParseInput<Rule>) -> ParseResult<()> {
         Ok(())
     }
-    fn merge(_: ParseInput<Rule>) -> ParseResult<()> {
+    fn arrow(_input: ParseInput<Rule>) -> ParseResult<()> {
         Ok(())
     }
-    fn assert(_: ParseInput<Rule>) -> ParseResult<()> {
+    fn merge(_input: ParseInput<Rule>) -> ParseResult<()> {
         Ok(())
     }
-    fn if_(_: ParseInput<Rule>) -> ParseResult<()> {
+    fn assert(_input: ParseInput<Rule>) -> ParseResult<()> {
         Ok(())
     }
-    fn in_(_: ParseInput<Rule>) -> ParseResult<()> {
+    fn if_(_input: ParseInput<Rule>) -> ParseResult<()> {
         Ok(())
     }
-    fn toMap(_: ParseInput<Rule>) -> ParseResult<()> {
+    fn toMap(_input: ParseInput<Rule>) -> ParseResult<()> {
         Ok(())
     }
 
+    #[alias(expression)]
     fn empty_list_literal<E: Clone>(
         input: ParseInput<Rule>,
     ) -> ParseResult<Expr<E>> {
-        let span = input.as_span();
         Ok(parse_children!(input;
-            [application_expression(e)] => {
-                spanned(span, EmptyListLit(e))
-            },
+            [expression(e)] => spanned(input.as_span(), EmptyListLit(e)),
         ))
     }
 
@@ -808,7 +780,7 @@ impl Parsers {
                     expression(right)] => {
                 spanned(span, BoolIf(cond, left, right))
             },
-            [let_binding(bindings).., in_(()), expression(final_expr)] => {
+            [let_binding(bindings).., expression(final_expr)] => {
                 bindings.rev().fold(
                     final_expr,
                     |acc, x| unspanned(Let(x.0, x.1, x.2, acc))
@@ -818,24 +790,22 @@ impl Parsers {
                     arrow(()), expression(body)] => {
                 spanned(span, Pi(l, typ, body))
             },
-            [operator_expression(typ), arrow(()), expression(body)] => {
+            [expression(typ), arrow(()), expression(body)] => {
                 spanned(span, Pi("_".into(), typ, body))
             },
-            [merge(()), import_expression(x), import_expression(y),
-                    application_expression(z)] => {
+            [merge(()), expression(x), expression(y), expression(z)] => {
                 spanned(span, Merge(x, y, Some(z)))
             },
-            [empty_list_literal(e)] => e,
             [assert(()), expression(x)] => {
                 spanned(span, Assert(x))
             },
-            [toMap(()), import_expression(x), application_expression(y)] => {
+            [toMap(()), expression(x), expression(y)] => {
                 spanned(span, ToMap(x, Some(y)))
             },
-            [operator_expression(e)] => e,
-            [operator_expression(e), expression(annot)] => {
+            [expression(e), expression(annot)] => {
                 spanned(span, Annot(e, annot))
             },
+            [expression(e)] => e,
         ))
     }
 
@@ -850,14 +820,8 @@ impl Parsers {
         ))
     }
 
-    fn List(_: ParseInput<Rule>) -> ParseResult<()> {
-        Ok(())
-    }
-    fn Optional(_: ParseInput<Rule>) -> ParseResult<()> {
-        Ok(())
-    }
-
-    #[prec_climb(application_expression, PRECCLIMBER)]
+    #[alias(expression, shortcut = true)]
+    #[prec_climb(expression, PRECCLIMBER)]
     fn operator_expression<E: Clone>(
         input: ParseInput<Rule>,
         l: Expr<E>,
@@ -886,55 +850,48 @@ impl Parsers {
         Ok(unspanned(BinOp(op, l, r)))
     }
 
-    fn Some_(_: ParseInput<Rule>) -> ParseResult<()> {
+    fn Some_(_input: ParseInput<Rule>) -> ParseResult<()> {
         Ok(())
     }
 
+    #[alias(expression, shortcut = true)]
     fn application_expression<E: Clone>(
         input: ParseInput<Rule>,
     ) -> ParseResult<Expr<E>> {
         Ok(parse_children!(input;
-            [first_application_expression(e)] => e,
-            [first_application_expression(first),
-                    import_expression(rest)..] => {
+            [expression(e)] => e,
+            [expression(first), expression(rest)..] => {
                 rest.fold(first, |acc, e| unspanned(App(acc, e)))
             },
         ))
     }
 
+    #[alias(expression, shortcut = true)]
     fn first_application_expression<E: Clone>(
         input: ParseInput<Rule>,
     ) -> ParseResult<Expr<E>> {
         let span = input.as_span();
         Ok(parse_children!(input;
-            [Some_(()), import_expression(e)] => {
+            [Some_(()), expression(e)] => {
                 spanned(span, SomeLit(e))
             },
-            [merge(()), import_expression(x), import_expression(y)] => {
+            [merge(()), expression(x), expression(y)] => {
                 spanned(span, Merge(x, y, None))
             },
-            [toMap(()), import_expression(x)] => {
+            [toMap(()), expression(x)] => {
                 spanned(span, ToMap(x, None))
             },
-            [import_expression(e)] => e,
-        ))
-    }
-
-    fn import_expression<E: Clone>(
-        input: ParseInput<Rule>,
-    ) -> ParseResult<Expr<E>> {
-        Ok(parse_children!(input;
-            [selector_expression(e)] => e,
-            [import(e)] => e,
+            [expression(e)] => e,
         ))
     }
 
+    #[alias(expression, shortcut = true)]
     fn selector_expression<E: Clone>(
         input: ParseInput<Rule>,
     ) -> ParseResult<Expr<E>> {
         Ok(parse_children!(input;
-            [primitive_expression(e)] => e,
-            [primitive_expression(first), selector(rest)..] => {
+            [expression(e)] => e,
+            [expression(first), selector(rest)..] => {
                 rest.fold(first, |acc, e| unspanned(match e {
                     Either::Left(l) => Field(acc, l),
                     Either::Right(ls) => Projection(acc, ls),
@@ -959,6 +916,7 @@ impl Parsers {
         ))
     }
 
+    #[alias(expression, shortcut = true)]
     fn primitive_expression<E: Clone>(
         input: ParseInput<Rule>,
     ) -> ParseResult<Expr<E>> {
@@ -969,46 +927,41 @@ impl Parsers {
             [integer_literal(n)] => spanned(span, IntegerLit(n)),
             [double_quote_literal(s)] => spanned(span, TextLit(s)),
             [single_quote_literal(s)] => spanned(span, TextLit(s)),
-            [empty_record_type(e)] => e,
-            [empty_record_literal(e)] => e,
-            [non_empty_record_type_or_literal(e)] => e,
-            [union_type(e)] => e,
-            [non_empty_list_literal(e)] => e,
-            [identifier(e)] => e,
             [expression(e)] => e,
         ))
     }
 
+    #[alias(expression)]
     fn empty_record_literal<E: Clone>(
         input: ParseInput<Rule>,
     ) -> ParseResult<Expr<E>> {
-        let span = input.as_span();
-        Ok(spanned(span, RecordLit(Default::default())))
+        Ok(spanned(input.as_span(), RecordLit(Default::default())))
     }
 
+    #[alias(expression)]
     fn empty_record_type<E: Clone>(
         input: ParseInput<Rule>,
     ) -> ParseResult<Expr<E>> {
-        let span = input.as_span();
-        Ok(spanned(span, RecordType(Default::default())))
+        Ok(spanned(input.as_span(), RecordType(Default::default())))
     }
 
+    #[alias(expression)]
     fn non_empty_record_type_or_literal<E: Clone>(
         input: ParseInput<Rule>,
     ) -> ParseResult<Expr<E>> {
-        let span = input.as_span();
-        Ok(parse_children!(input;
+        let e = parse_children!(input;
             [label(first_label), non_empty_record_type(rest)] => {
                 let (first_expr, mut map) = rest;
                 map.insert(first_label, first_expr);
-                spanned(span, RecordType(map))
+                RecordType(map)
             },
             [label(first_label), non_empty_record_literal(rest)] => {
                 let (first_expr, mut map) = rest;
                 map.insert(first_label, first_expr);
-                spanned(span, RecordLit(map))
+                RecordLit(map)
             },
-        ))
+        );
+        Ok(spanned(input.as_span(), e))
     }
 
     fn non_empty_record_type<E: Clone>(
@@ -1047,19 +1000,16 @@ impl Parsers {
         ))
     }
 
+    #[alias(expression)]
     fn union_type<E: Clone>(input: ParseInput<Rule>) -> ParseResult<Expr<E>> {
-        let span = input.as_span();
-        Ok(parse_children!(input;
-            [empty_union_type(_)] => {
-                spanned(span, UnionType(Default::default()))
-            },
-            [union_type_entry(entries)..] => {
-                spanned(span, UnionType(entries.collect()))
-            },
-        ))
+        let map = parse_children!(input;
+            [empty_union_type(_)] => Default::default(),
+            [union_type_entry(entries)..] => entries.collect(),
+        );
+        Ok(spanned(input.as_span(), UnionType(map)))
     }
 
-    fn empty_union_type(_: ParseInput<Rule>) -> ParseResult<()> {
+    fn empty_union_type(_input: ParseInput<Rule>) -> ParseResult<()> {
         Ok(())
     }
 
@@ -1072,13 +1022,13 @@ impl Parsers {
         ))
     }
 
+    #[alias(expression)]
     fn non_empty_list_literal<E: Clone>(
         input: ParseInput<Rule>,
     ) -> ParseResult<Expr<E>> {
-        let span = input.as_span();
         Ok(parse_children!(input;
             [expression(items)..] => spanned(
-                span,
+                input.as_span(),
                 NEListLit(items.collect())
             )
         ))