1 files changed, 20 insertions, 0 deletions
diff --git a/test-suite/bugs/closed/4216.v b/test-suite/bugs/closed/4216.v
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+++ b/test-suite/bugs/closed/4216.v
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+Generalizable Variables T A.
+
+Inductive path `(a: A): A -> Type := idpath: path a a.
+
+Class TMonad (T: Type -> Type) := {
+  bind: forall {A B: Type}, (T A) -> (A -> T B) -> T B;
+  ret: forall {A: Type}, A -> T A;
+  ret_unit_left: forall {A B: Type} (k: A -> T B) (a: A),
+                 path (bind (ret a) k) (k a)
+  }.
+
+Let T_fzip `{TMonad T} := fun (A B: Type) (f: T (A -> B)) (t: T A)
+                  => bind t (fun a => bind f (fun g => ret (g a) )).
+Let T_pure `{TMonad T} := @ret _ _.
+
+Let T_pure_id `{TMonad T} {A: Type} (t: A -> A) (x: T A): 
+        path (T_fzip A A (T_pure (A -> A) t) x) x.
+  unfold T_fzip, T_pure.
+  Fail rewrite (ret_unit_left (fun g a => ret (g a)) (fun x => x)).
+