elem (1,2,3) [(1,2,3)] -> works (true)
elem (1,2,_) [(1,2,3)] -> doesnt work (want it return true as well)
What Im trying to do is if the first two elements of tuple matches one in the list return true.
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i mean how can i make it work.thetux4– thetux42011-06-03 13:35:50 +00:00Commented Jun 3, 2011 at 13:35
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2I believe the question is: Is there a way to do partial matches on tuples like you would do full matches with the elem function.stonemetal– stonemetal2011-06-03 13:45:00 +00:00Commented Jun 3, 2011 at 13:45
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2 Answers
You can use the prelude function any to find out whether at least one element in a list meets a given condition (the condition in this case being "it matches the pattern (1, 2, _)").
An example for this case would be:
any (\x -> case x of (1,2,_) -> True; _ -> False) [(1,2,3),(4,5,6)]
Or a bit more concisely:
or [True | (1,2,x) <- [(1,2,3),(4,5,6)]]
2 Comments
thetux4
can you give an example usage?
Jeff Foster
matchElem (r,s,_) = any (\(a,b,_) -> a == r && b == s)You can use elem if convert the triples to pairs first:
elem (1,2) $ map (\(a,b,_) -> (a,b)) [(1,2,3),(4,5,6)]
