Add IdfunWithAlt

1 files changed, 44 insertions, 0 deletions

diff --git a/src/Util/IdfunWithAlt.v b/src/Util/IdfunWithAlt.v
new file mode 100644
index 000000000..ed7a82ace
--- /dev/null
+++ b/src/Util/IdfunWithAlt.v
@@ -0,0 +1,44 @@
+(** Some constants that return their first argument, and hold an equal second argument. *)
+Require Import Crypto.Util.Tuple.
+Definition id_with_alt {A} (value : A) (value_for_alt : A) : A
+:= value.
+Definition id_with_alt_proof {A} (value : A) (value_for_alt : A)
+           {pf : value = value_for_alt}
+  : A
+  := id_with_alt value value_for_alt.
+Fixpoint id_tuple'_with_alt {A n}
+         {struct n}
+  : forall (value value_for_alt : tuple' A n),
+    tuple' A n
+  := match n return forall value value_for_alt : tuple' A n, tuple' A n with
+     | O => id_with_alt
+     | S n' => fun (value value_for_alt : tuple' A n' * A)
+               => (@id_tuple'_with_alt A n' (fst value) (fst value_for_alt),
+                   @id_with_alt A (snd value) (snd value_for_alt))
+     end.
+Fixpoint id_tuple'_with_alt_proof {A n}
+         {struct n}
+  : forall (value value_for_alt : tuple' A n) {pf : value = value_for_alt},
+    tuple' A n
+  := match n return forall value value_for_alt : tuple' A n, _ -> tuple' A n with
+     | O => id_with_alt_proof
+     | S n' => fun (value value_for_alt : tuple' A n' * A) (pf : value = value_for_alt)
+               => (@id_tuple'_with_alt_proof A n' (fst value) (fst value_for_alt)
+                                             (f_equal (@fst _ _) pf),
+                   @id_with_alt_proof A (snd value) (snd value_for_alt)
+                                      (f_equal (@snd _ _) pf))
+     end.
+Definition id_tuple_with_alt {A n}
+  : forall (value value_for_alt : tuple A n), tuple A n
+  := match n with
+     | O => id_with_alt
+     | S n' => id_tuple'_with_alt
+     end.
+Fixpoint id_tuple_with_alt_proof {A n}
+         {struct n}
+  : forall (value value_for_alt : tuple A n) {pf : value = value_for_alt},
+    tuple A n
+  := match n with
+     | O => id_with_alt_proof
+     | S n' => id_tuple'_with_alt_proof
+     end.