content: {-
  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.
  -}
  