If you add a third pattern, you can see exactly what it's failing to match:<br><br> kmerge x = error (show x)<br><br>In order to do this, you just need to add Show constraints for a and b in the type of kmerge:<br><br>
kmerge :: (Show a, Show b, Eq a) => [(a,[b])]->[(a,[b])]<br>
<br>You'll find that the pattern that it's failing to match is:<br><br> [('b',[5,4]),('b',[1]),('b',[6])]<br><br>Because you combined 5 and 4 and passed that on to your recursive 'kmerge' call. Your patterns only cover the case where there is exactly one element in the list.
<br><br>- Phil<br><br><div class="gmail_quote">On Dec 6, 2007 9:39 AM, georg86 <<a href="mailto:georg_straube@web.de">georg_straube@web.de</a>> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<br>Hello!<br>I need to write a function which should is supposed to merge multiple<br>entries with the same<br>key (out of a sorted key-value-list) into one single entry.<br>However, I keep getting a pattern matching error.
<br><br>(For example, for input [('b',[5]),('b',[4]),('b',[1]),('b',[6])]:<br>"Program error: pattern match failure: kgroup<br>[('b',[5,4]),('b',[1]),('b',[6])]")
<br><br>Thank you very much for your help.<br><br>kmerge::Eq a => [(a,[b])]->[(a,[b])]<br><br>kmerge [] = []<br><br>kmerge ((x,[y]):[]) = [(x,[y])]<br><br>kmerge ((x,[y]):(u,[v]):xs) | x == u = kmerge ((x,[y,v]):xs)
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