Fix let variable typing rules

cranelift/isle/isle/src/sema.rs

@@ -1251,7 +1251,7 @@ impl TermEnv {
                     };
 
                     // Evaluate the variable's value.
-                    let val = Box::new(match self.translate_expr(tyenv, &def.val, ty, bindings) {
+                    let val = Box::new(match self.translate_expr(tyenv, &def.val, tid, bindings) {
                         Some(e) => e,
                         None => {
                             // Keep going for more errors.

cranelift/isle/isle_examples/let.isle

@@ -0,0 +1,21 @@
+(type u32 (primitive u32))
+(type A (enum (Add (x u32) (y u32)) (Sub (x u32) (y u32))))
+(type B (enum (B (z u32))))
+
+(decl Sub (u32 u32) u32)
+(extern constructor Sub sub)
+
+(decl Add (u32 u32) u32)
+(extern constructor Add add)
+
+(decl Lower (A) B)
+
+(rule
+  (Lower (A.Add x y))
+  (let ((z u32 (Add x y)))
+    (B.B z)))
+
+(rule
+  (Lower (A.Sub x y))
+  (let ((z u32 (Sub x y)))
+    (B.B z)))