{-
From: Paul Sanders <psanders@srd.bt.co.uk>
To: partain
Subject: A puzzle for you
Date: Mon, 28 Oct 91 17:02:19 GMT

I'm struggling with the following code fragment at the moment:
-}

import Data.Array -- 1.3
import Data.Ix    -- 1.3

conv_list :: (Ix a, Ix b) => [a] -> [b] -> [[c]] -> Array (a,b) c -> Array (a,b) c
conv_list [] _ _ ar = ar
conv_list _ _ [] ar = ar
conv_list (r:rs) cls (rt:rts) ar
      = conv_list rs cls rts ar'
        where ar' = conv_elems r cls rt ar

conv_elems :: (Ix a, Ix b) => a -> [b] -> [c] -> Array (a,b) c -> Array (a,b) c
conv_elems row [] _ ar = ar
conv_elems _ _ [] ar = ar
conv_elems row (col:cls) (rt:rts) ar
      = conv_elems row cls rts ar'
        where ar' = ar // [((row,col), rt)]

ar :: Array (Int, Int) Int
ar = conv_list [(1::Int)..(3::Int)] [(1::Int)..(3::Int)] ar_list init_ar
     where init_ar = array (((1::Int),(1::Int)),((3::Int),(3::Int))) []


ar_list :: [[Int]] -- WDP
ar_list = [[1,2,3],
           [6,7,8],
           [10,12,15]]

main = putStrLn (show ar)

{-
What it tries to do is turn a list of lists into a 2-d array in an incremental
fashion using 2 nested for-loops. It compiles okay on the prototype compiler
but gives a segmentation fault when it executes. I know I can define in the
array in one go (and I have done) but, for my piece of mind, I want to get this
way working properly.

Is it a bug in the prototype or is there a glaringly obvious error in my code
which I've been stupid to spot ????

Hoping its the latter,

Paul.
-}