[MLton-commit] r6514

[Vesa Karvonen]

Added filter to monad with plus, which makes sense if the monad with plus
satisfies the "left distribution" law.  In fact, it might make sense to
introduce a separate signature for monad with or (as opposed to monad with
plus) that satisfies the "left catch" law, but not the "left distribution"
law.

----------------------------------------------------------------------

U   mltonlib/trunk/com/ssh/extended-basis/unstable/detail/concept/mk-monad.fun
U   mltonlib/trunk/com/ssh/extended-basis/unstable/public/concept/monad.sig

----------------------------------------------------------------------

Modified: mltonlib/trunk/com/ssh/extended-basis/unstable/detail/concept/mk-monad.fun
===================================================================
--- mltonlib/trunk/com/ssh/extended-basis/unstable/detail/concept/mk-monad.fun	2008-03-29 11:58:47 UTC (rev 6513)
+++ mltonlib/trunk/com/ssh/extended-basis/unstable/detail/concept/mk-monad.fun	2008-03-29 12:06:04 UTC (rev 6514)
@@ -1,4 +1,4 @@
-(* Copyright (C) 2007 SSH Communications Security, Helsinki, Finland
+(* Copyright (C) 2007-2008 SSH Communications Security, Helsinki, Finland
  *
  * This code is released under the MLton license, a BSD-style license.
  * See the LICENSE file or http://mlton.org/License for details.
@@ -74,13 +74,15 @@
 end
 
 functor MkMonadP (Core : MONADP_CORE) : MONADP = struct
-   infix <|>
+   infix <|> >>=
    structure Monad = MkMonad (Core)
    open Monad Core
    type 'a monadp_ex = 'a monad
 
    fun guard b = if b then return () else zero
 
+   fun filter p m = m >>= (fn x => if p x then return x else zero)
+
    fun sumWith x2yM =
     fn []    => zero
      | [x]   => x2yM x

Modified: mltonlib/trunk/com/ssh/extended-basis/unstable/public/concept/monad.sig
===================================================================
--- mltonlib/trunk/com/ssh/extended-basis/unstable/public/concept/monad.sig	2008-03-29 11:58:47 UTC (rev 6513)
+++ mltonlib/trunk/com/ssh/extended-basis/unstable/public/concept/monad.sig	2008-03-29 12:06:04 UTC (rev 6514)
@@ -1,4 +1,4 @@
-(* Copyright (C) 2007 SSH Communications Security, Helsinki, Finland
+(* Copyright (C) 2007-2008 SSH Communications Security, Helsinki, Finland
  *
  * This code is released under the MLton license, a BSD-style license.
  * See the LICENSE file or http://mlton.org/License for details.
@@ -107,6 +107,7 @@
 signature MONADP_EX = sig
    type 'a monadp_ex
    val guard : Bool.t -> Unit.t monadp_ex
+   val filter : 'a UnPr.t -> 'a monadp_ex UnOp.t
    val sum : 'a monadp_ex List.t -> 'a monadp_ex
    val sumWith : ('a -> 'b monadp_ex) -> 'a List.t -> 'b monadp_ex
 end