[Newbie] Programming with MArray

[José Romildo Malaquias]

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Hello.

To learn how to program with muttable arrays in Haskell, I have done
a very simple program to sum two arrays. I am submitting it to this
group so that it can be reviewd and commented. I have not find
examples on how to program with muttable arrays.

I would like for instance to see comments on the way the
iteration over the array indices was done: using a list
of indices. I looked for a way of incrementting an
index, starting from the lower bound towards the upper
bound, but failed in finding it. Is there other ways of
iterating over the muttable array other then using
its list of indices?

Regards,

Romildo
-- 
Prof. José Romildo Malaquias               Departamento de Computação
http://iceb.ufop.br/~romildo       Universidade Federal de Ouro Preto
romildo@iceb.ufop.br                                           Brasil
romildo@uber.com.br

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module Main where

import MArray
import ST

addArray :: (Ix ix, Num a) =>
	    STArray s ix a -> STArray s ix a -> STArray s ix a -> ST s ()

addArray v1 v2 v3
    | b1 == b2 && b1 == b3 = mapM_ update (indices v1)
    | otherwise            = error "Bounds mismatch in addArray"
    where
    b1 = bounds v1
    b2 = bounds v2
    b3 = bounds v3
    update i = do x1 <- readArray v1 i
		  x2 <- readArray v2 i
		  writeArray v3 i (x1 + x2)

testAddArray = do v1 <- newListArray (1,10) [0..10]
		  v2 <- newListArray (1,10) [1..10]
		  v3 <- newArray_ (1,10)
		  addArray v1 v2 v3
		  getElems v3

main = do xs <- stToIO testAddArray
	  print xs

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