[Haskell-cafe] Pattern matching error

georg86 georg_straube at web.de
Thu Dec 6 12:39:05 EST 2007

I need to write a function which should is supposed to merge multiple
entries with the same
key (out of a sorted key-value-list) into one single entry.
However, I keep getting a pattern matching error.

(For example, for input [('b',[5]),('b',[4]),('b',[1]),('b',[6])]: 
"Program error: pattern match failure: kgroup

Thank you very much for your help.

kmerge::Eq a => [(a,[b])]->[(a,[b])]

kmerge [] = []

kmerge ((x,[y]):[]) = [(x,[y])]

kmerge ((x,[y]):(u,[v]):xs) | x == u = kmerge ((x,[y,v]):xs) 
                                     | otherwise = (x,[y]):(u,[v]):kmerge xs
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