add crude Monad type class

[coq-hetmet.git] / src / General.v

diff --git a/src/General.v b/src/General.v
index 7af1fc3..7e0af43 100644 (file)
--- a/src/General.v
+++ b/src/General.v
@@ -629,6 +629,16 @@ CoInductive Fresh A T :=
 Definition map2 {A}{B}(f:A->B)(t:A*A) : (B*B) := ((f (fst t)), (f (snd t))).
 
 
+(* string stuff *)
+Variable eol : string.
+Extract Constant eol  => "'\n':[]".
+
+Class Monad {T:Type->Type} :=
+{ returnM : forall {a},     a -> T a
+; bindM   : forall {a}{b},  T a -> (a -> T b) -> T b
+}.
+Implicit Arguments Monad [ ].
+Notation "a >>>= b" := (@bindM _ _ _ _ a b) (at level 50, left associativity).
 
 (* the Error monad *)
 Inductive OrError (T:Type) :=
@@ -645,6 +655,18 @@ Definition orErrorBind {T:Type} (oe:OrError T) {Q:Type} (f:T -> OrError Q) :=
   end.
 Notation "a >>= b" := (@orErrorBind _ a _ b) (at level 20).
 
+Open Scope string_scope.
+Definition orErrorBindWithMessage {T:Type} (oe:OrError T) {Q:Type} (f:T -> OrError Q) err_msg :=
+  match oe with
+    | Error s => Error (err_msg +++ eol +++ "  " +++ s)
+    | OK    t => f t
+  end.
+
+Notation "a >>=[ S ] b" := (@orErrorBindWithMessage _ a _ b S) (at level 20).
+
+Definition addErrorMessage s {T} (x:OrError T) :=
+  x >>=[ s ] (fun y => OK y).
+
 Inductive Indexed {T:Type}(f:T -> Type) : ???T -> Type :=
 | Indexed_Error : forall error_message:string, Indexed f (Error error_message)
 | Indexed_OK    : forall t, f t -> Indexed f (OK t)
@@ -693,3 +715,5 @@ Lemma list2vecOrFail {T}(l:list T)(n:nat)(error_message:nat->nat->string) : ???(
     rewrite e in v; apply OK; apply v.
     apply (Error (error_message (length l) n)).
     Defined.
+
+