Re[2]: [Haskell-cafe] A bug of groupBy implement

Hello Stephen, Monday, December 7, 2009, 8:11:01 PM, you wrote: it's just what goupBy compares with the first element of group rather than comparing two adjancent elements. look at the trace it's not a bug, but misunderstanding of specification :)

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 :

...

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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