2 files changed, 22 insertions, 2 deletions
diff --git a/dhall/src/syntax/ast/expr.rs b/dhall/src/syntax/ast/expr.rs
index 8023771..b53e6cb 100644
--- a/dhall/src/syntax/ast/expr.rs
+++ b/dhall/src/syntax/ast/expr.rs
@@ -258,8 +258,8 @@ impl Expr {
 }
 
 // Empty enum to indicate that no error can occur
-enum X {}
-fn trivial_result<T>(x: Result<T, X>) -> T {
+pub(crate) enum X {}
+pub(crate) fn trivial_result<T>(x: Result<T, X>) -> T {
     match x {
         Ok(x) => x,
         Err(e) => match e {},
diff --git a/dhall/src/syntax/ast/import.rs b/dhall/src/syntax/ast/import.rs
index 75d7946..c45fe51 100644
--- a/dhall/src/syntax/ast/import.rs
+++ b/dhall/src/syntax/ast/import.rs
@@ -1,3 +1,5 @@
+use crate::syntax::trivial_result;
+
 /// The beginning of a file path which anchors subsequent path components
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum FilePrefix {
@@ -75,6 +77,12 @@ impl<SE> URL<SE> {
             headers,
         })
     }
+    pub fn map_ref<'a, SE2>(
+        &'a self,
+        f: impl FnOnce(&'a SE) -> SE2,
+    ) -> URL<SE2> {
+        trivial_result(self.traverse_ref(|x| Ok(f(x))))
+    }
 }
 
 impl<SE> ImportTarget<SE> {
@@ -90,6 +98,12 @@ impl<SE> ImportTarget<SE> {
             Missing => Missing,
         })
     }
+    pub fn map_ref<'a, SE2>(
+        &'a self,
+        f: impl FnOnce(&'a SE) -> SE2,
+    ) -> ImportTarget<SE2> {
+        trivial_result(self.traverse_ref(|x| Ok(f(x))))
+    }
 }
 
 impl<SE> Import<SE> {
@@ -103,4 +117,10 @@ impl<SE> Import<SE> {
             hash: self.hash.clone(),
         })
     }
+    pub fn map_ref<'a, SE2>(
+        &'a self,
+        f: impl FnOnce(&'a SE) -> SE2,
+    ) -> Import<SE2> {
+        trivial_result(self.traverse_ref(|x| Ok(f(x))))
+    }
 }