[Haskell-cafe] A bug of groupBy implement

Stephen Tetley stephen.tetley at gmail.com
Mon Dec 7 12:11:01 EST 2009


Could it not be a bug in

a) printf
b) unsafePerformIO
c) >>
d) return
e) <=
f) show
g) GHC or GHCi?

All of the above?

Best wishes

Stephen

2009/12/7 L.Guo <leaveye.guo at gmail.com>:
> Hi there:
>
> My friend asked me a question, and i suppose he has found a bug of `groupBy'.
>
> Here is the code piece:
>
>> List.groupBy (\a b -> Foreign.unsafePerformIO (Text.Printf.printf "\t%d <= %d ?: %s\n" a b (show (a<=b)) >> return (a<=b))) [7,3,5,9,6,8,3,5,4]
>
> I have tested it in GHC 6.10.4 (Win XP) and GHC 6.8.3 (Linux), both give the wrong result (categaried):
>
>        7 <= 3 ?: False
>        3 <= 5 ?: True
>        3 <= 9 ?: True
>        3 <= 6 ?: True
>        3 <= 8 ?: True
>        3 <= 3 ?: True
>        3 <= 5 ?: True
>        3 <= 4 ?: True
> [[7],[3,5,9,6,8,3,5,4]]
>
>
>    Regards
> --------------
> L.Guo
> 2009-12-08
>
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