1 files changed, 84 insertions, 0 deletions
diff --git a/src/Util/ListUtil.v b/src/Util/ListUtil.v
new file mode 100644
index 000000000..5604ebcc3
--- /dev/null
+++ b/src/Util/ListUtil.v
@@ -0,0 +1,84 @@
+Require Import List.
+Require Import Omega.
+Require Import Arith.Peano_dec.
+
+Ltac nth_tac' := 
+  intros; simpl in *; unfold error,value in *; repeat progress (match goal with
+    | [  |- context[match nth_error ?xs ?i with Some _ => _ | None => _ end ] ] => case_eq (nth_error xs i); intros
+    | [ |- context[(if lt_dec ?a ?b then _ else _) = _] ] => destruct (lt_dec a b)
+    | [ |- context[_ = (if lt_dec ?a ?b then _ else _)] ] => destruct (lt_dec a b)
+    | [ H: context[(if lt_dec ?a ?b then _ else _) = _] |- _ ] => destruct (lt_dec a b)
+    | [ H: context[_ = (if lt_dec ?a ?b then _ else _)] |- _ ] => destruct (lt_dec a b)
+    | [ H: _ /\ _ |- _ ] => destruct H
+    | [ H: Some _ = Some _ |- _ ] => injection H; clear H; intros; subst
+    | [ H: None = Some _  |- _ ] => inversion H
+    | [ H: Some _ = None |- _ ] => inversion H
+    | [ |- Some _ = Some _ ] => apply f_equal
+  end); eauto; try (autorewrite with list in *); try omega; eauto.
+Lemma nth_error_map : forall A B (f:A->B) i xs y,
+  nth_error (map f xs) i = Some y ->
+  exists x, nth_error xs i = Some x /\ f x = y.
+Proof.
+  induction i; destruct xs; nth_tac'.
+Qed.
+
+Lemma nth_error_seq : forall i start len,
+  nth_error (seq start len) i =
+  if lt_dec i len
+  then Some (start + i)
+  else None.
+  induction i; destruct len; nth_tac'; erewrite IHi; nth_tac'.
+Qed.
+
+Lemma nth_error_length_error : forall A i (xs:list A), nth_error xs i = None ->
+  i >= length xs.
+Proof.
+  induction i; destruct xs; nth_tac'; try specialize (IHi _ H); omega.
+Qed.
+
+Ltac nth_tac := 
+  repeat progress (try nth_tac'; try (match goal with
+    | [ H: nth_error (map _ _) _ = Some _ |- _ ] => destruct (nth_error_map _ _ _ _ _ _ H); clear H
+    | [ H: nth_error (seq _ _) _ = Some _ |- _ ] => rewrite nth_error_seq in H
+    | [H: nth_error _ _ = None |- _ ] => specialize (nth_error_length_error _ _ _ H); intro; clear H
+  end)).
+
+Lemma app_cons_app_app : forall T xs (y:T) ys, xs ++ y :: ys = (xs ++ (y::nil)) ++ ys.
+Proof.
+  induction xs; simpl; repeat match goal with
+           | [ H : _ |- _ ] => rewrite H; clear H
+           | _ => progress intuition
+         end; eauto.
+Qed.
+
+(* xs[n] := x *)
+Fixpoint set_nth {T} n x (xs:list T) {struct n} :=
+	match n with
+	| O => match xs with
+				 | nil => nil
+				 | x'::xs' => x::xs'
+				 end
+	| S n' =>  match xs with
+				 | nil => nil
+				 | x'::xs' => x'::set_nth n' x xs'
+				 end
+  end.
+
+Lemma nth_set_nth : forall m {T} (xs:list T) (n:nat) (x x':T),
+  nth_error (set_nth m x xs) n =
+  if eq_nat_dec n m
+  then (if lt_dec n (length xs) then Some x else None)
+  else nth_error xs n.
+Proof.
+	induction m.
+
+	destruct n, xs; auto.
+
+	intros; destruct xs, n; auto.
+	simpl; unfold error; match goal with
+		[ |- None = if ?x then None else None ] => destruct x
+	end; auto.
+
+	simpl nth_error; erewrite IHm by auto; clear IHm.
+	destruct (eq_nat_dec n m), (eq_nat_dec (S n) (S m)); nth_tac.
+Qed.