--------------------------------------------------------------------------------
--  $Id: AccumulateM.hs,v 1.2 2003/09/24 18:50:52 graham Exp $
--
--  Copyright (c) 2003, G. KLYNE.  All rights reserved.
--  See end of this file for licence information.
--------------------------------------------------------------------------------
-- |
--  Module      :  AccummulateM
--  Copyright   :  (c) 2003, Graham Klyne
--  License     :  GPL V2
--
--  Maintainer  :  Graham Klyne
--  Stability   :  provisional
--  Portability :  H98
--
--  This module defines a monadic accumulator type.  The plan is that it be
--  used in conjunction with FunctorM and similar constructs to accumulate
--  some or all of the values visited.
--
--------------------------------------------------------------------------------

module Accumulator
    ( Accumulator(..)
    )
where

import Monad
    ( foldM )

{-
class (Monad m) => MonadAccum m c e where
    seedVal :: m c
    growVal :: c -> e -> m c
    reapVal :: m c -> c
-}

data Accumulator c = Accumulator c deriving Show

instance Monad Accumulator where
    (Accumulator v) >>= k  = k v
    return v               = Accumulator v

instance MonadAccum Accumulator Int Int where
    seedVal                 = Accumulator 0
    growVal n m             = Accumulator (n+m)
    reapVal (Accumulator n) = n

{-
instance MonadAccum Accumulator Integer Integer where
    seedVal                 = Accumulator 0
    growVal n m             = Accumulator (n+m)
    reapVal (Accumulator n) = n
-}

{-
instance MonadAccum Accumulator [v] v where
    seedVal                  = Accumulator []
    growVal vs v             = Accumulator (v:vs)
    reapVal (Accumulator vs) = vs
-}

seedVal                  = Accumulator []
growVal vs v             = Accumulator (v:vs)
reapVal (Accumulator vs) = vs

--  Tests

addVal :: Int -> Int -> (Accumulator Int)
addVal m n = Accumulator (n+m)

testList = [1,2,3,4,5,6] :: [Int]

test1 = foldM addVal 0 testList
test2 = Accumulator 0
test3 = (Accumulator 0) >>= addVal 1
test4 = (Accumulator 5) >>= addVal 5
test5 = growVal 1 :: Int -> Accumulator Int
test6 = foldM (growVal (Accumulator 0)) testList

--------------------------------------------------------------------------------
--
--  Copyright (c) 2003, G. KLYNE.  All rights reserved.
--
--  This file is part of Swish.
--
--  Swish is free software; you can redistribute it and/or modify
--  it under the terms of the GNU General Public License as published by
--  the Free Software Foundation; either version 2 of the License, or
--  (at your option) any later version.
--
--  Swish is distributed in the hope that it will be useful,
--  but WITHOUT ANY WARRANTY; without even the implied warranty of
--  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
--  GNU General Public License for more details.
--
--  You should have received a copy of the GNU General Public License
--  along with Swish; if not, write to:
--    The Free Software Foundation, Inc.,
--    59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
--
--------------------------------------------------------------------------------
-- $Source: /file/cvsdev/HaskellRDF/AccumulateM.hs,v $
-- $Author: graham $
-- $Revision: 1.2 $
-- $Log: AccumulateM.hs,v $
-- Revision 1.2  2003/09/24 18:50:52  graham
-- Revised module format to be Haddock compatible.
--
-- Revision 1.1  2003/06/12 00:49:04  graham
-- Basic query processor runs test cases OK.
-- Proof framework compiles, not yet tested.
--