Add HeadUnderBinders

1 files changed, 22 insertions, 0 deletions

diff --git a/src/Util/Tactics/HeadUnderBinders.v b/src/Util/Tactics/HeadUnderBinders.v
new file mode 100644
index 000000000..a111a045f
--- /dev/null
+++ b/src/Util/Tactics/HeadUnderBinders.v
@@ -0,0 +1,22 @@
+Require Export Crypto.Util.FixCoqMistakes.
+
+(** find the head of the given expression, underneath [fun] and [forall] *)
+Ltac head_under_binders_gen redtac expr :=
+  let expr := redtac expr in
+  match expr with
+  | ?f _ => head_under_binders_gen redtac f
+  | fun x : ?T => @?f x
+    => lazymatch constr:(fun x : T
+                         => ltac:(let f' := (eval cbv beta in (f x)) in
+                                  let h := head_under_binders_gen redtac f' in
+                                  exact h)) with
+       | fun _ => ?f => f
+       | ?f => f
+       end
+  | forall x, @?f x
+    => head_under_binders_gen redtac f
+  | ?expr => expr
+  end.
+
+Ltac head_under_binders expr := head_under_binders_gen ltac:(fun e => e) expr.
+Ltac head_hnf_under_binders expr := head_under_binders_gen ltac:(fun e => eval hnf in e) expr.