Factor out shift/subst/shift dance

1 files changed, 1 insertions, 4 deletions

diff --git a/dhall/src/typecheck.rs b/dhall/src/typecheck.rs
index 75e6e1d..145de63 100644
--- a/dhall/src/typecheck.rs
+++ b/dhall/src/typecheck.rs
@@ -268,10 +268,7 @@ where
             let tA2 = normalized_type_with(ctx, a.clone())?;
             if prop_equal(tA.as_ref(), tA2.as_ref()) {
                 let vx0 = &V(x.clone(), 0);
-                let a2 = shift(1, vx0, a);
-                let tB2 = subst(vx0, &a2, &tB);
-                let tB3 = shift(-1, vx0, &tB2);
-                return Ok(tB3);
+                return Ok(subst_shift(vx0, &a, &tB));
             } else {
                 Err(mkerr(TypeMismatch(f.clone(), tA, a.clone(), tA2)))
             }