[Haskell-cafe] Pattern matching problems

[Marcin Tustin]

    In case I confused anyone, this is a separate issue. Thanks for your attention and help.

On Sat, Sep 24, 2005 at 01:20:22AM +0100, Marcin Tustin wrote:
> 
> For some reason the following code is producing an error message from ghci that the the patterns are non-exhaustive. Does anyone have any idea why that could be, given that the patterns are, at least in my meaning, provably exhaustive?
> 
> choosenonuniqueset n (a:r)
>     | (length r) >  (n-1) = [ (sort (a:x)) | x <- (choosenonuniqueset (n-1) r)] 
>                             `union`
>                             [ (sort (a:x)) | x <- (choosenonuniqueset n r)]
>     | (length r) == (n-1) = [a:r]
>     | (length r) <  (n-1) = []
> 
> Error message is:
> 
> *Main> :reload
> Compiling Main             ( birthday.hs, interpreted )
> Ok, modules loaded: Main.
> *Main> choosenonuniqueset 2 [1..5]
> *** Exception: birthday.hs:(22,0)-(27,29): Non-exhaustive patterns in function choosenonuniqueset
> 
> *Main> choosenonuniqueset 5 [1..5]
> [[1,2,3,4,5]]
> *Main>
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