2 files changed, 18 insertions, 0 deletions
diff --git a/dhall/src/lib.rs b/dhall/src/lib.rs
index 4238b6e..f3a11a1 100644
--- a/dhall/src/lib.rs
+++ b/dhall/src/lib.rs
@@ -99,6 +99,11 @@ impl Parsed {
     pub fn to_expr(&self) -> Expr {
         self.0.clone()
     }
+
+    pub fn substitute_name(self, label: syntax::Label, value: Expr) -> Parsed {
+        let Parsed (expr, import_location) = self;
+        Parsed (expr.substitute_name(label, value), import_location)
+    }
 }
 
 impl<'cx> Resolved<'cx> {
diff --git a/dhall/src/syntax/ast/expr.rs b/dhall/src/syntax/ast/expr.rs
index eba2735..bc3ffa4 100644
--- a/dhall/src/syntax/ast/expr.rs
+++ b/dhall/src/syntax/ast/expr.rs
@@ -182,6 +182,19 @@ impl Expr {
         let data = binary::encode(self)?;
         Ok(crate::utils::sha256_hash(&data))
     }
+
+    /// this wraps the expression into an additional let-binding
+    pub fn substitute_name(self, label: Label, value: Expr) -> Expr {
+        Expr::new(
+            ExprKind::Let(
+                label,
+                None,
+                value,
+                self
+            ),
+            Span::Artificial
+        )
+    }
 }
 
 // Empty enum to indicate that no error can occur