problems with Array.elems in ghc-5.02

[Bostjan Slivnik]

Hi,

I am afraid I have to report a bug in the Array module which is a part
of ghc-5.02.  Consider the following program:

   module Main where

   import Array
   import List

   data Foo = Foo Int [Foo]

   instance Eq Foo  where (==)    (Foo f1 _) (Foo f2 _) = (==)    f1 f2
   instance Ord Foo where compare (Foo f1 _) (Foo f2 _) = compare f1 f2

   instance Ix Foo where
    range (lo@(Foo _ foos),hi) = (filter ((<=)lo).filter ((>=)hi)) foos
    inRange (Foo lo _,Foo hi _) (Foo f _) = inRange (lo,hi) f
    index _ (Foo f _) = f

   instance Show Foo where showsPrec _ (Foo f _) = shows f

   lstOfFoos = [Foo f lstOfFoos|f<-[2..5]]
   arrOfFoos = array (head lstOfFoos,last lstOfFoos) (zip lstOfFoos lstOfFoos)

   main :: IO ()
   main = do putStr (show lstOfFoos); putStr "\n"
	     putStr (show ((length.indices) arrOfFoos)); putStr "\n"
             putStr (show ((length.elems  ) arrOfFoos)); putStr "\n"
             putStr (show ((indices) arrOfFoos)); putStr "\n"
             putStr (show ((elems  ) arrOfFoos)); putStr "\n"

It works fine when compiled with ghc-5.00.2, but when compiled with
ghc-5.02 the last `putStr' crashes with

   Fail: (Array.!): undefined array element

The length of the elements, as it is printed out, equals the length of
the indices plus the lower bound of the interval, in this case 2.
Hence, if the list `[2..5]' is replaced with `[0..3]', the program
works find with both version of the compiler.

(This can be reproduced on RedHat 7.1 using Chakravarty's binary rpms.)

Cheers, Bo"stjan