Hello! 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 [('b',[5,4]),('b',[1]),('b',[6])]") 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 -- View this message in context: http://www.nabble.com/Pattern-matching-error-tf4957268.html#a14196413 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.