On Wed, Jul 11, 2007 at 10:31:36PM +0200, Hugh Perkins wrote:
Ok so I played with the tweaked problem (Unix 'uniq'), and getting it to be lazy. This seems to work:
It's slightly worse than that: unix uniq only eliminates *consecutive* identical lines from its input. If you want to eliminate all duplicates, you have to pipe your input through sort first.
testunique :: Eq a => [a] -> [a] testunique list = testunique' list [] where testunique' :: Eq a => [a] -> [a] -> [a] testunique' [] elementssofar = [] testunique' (x:xs) elementssofar | x `elem` elementssofar = (testunique' elementssofar xs) | otherwise = x : ( testunique' xs (x:elementssofar))
I suspect the author upthread had something more like this in mind: uniq :: Eq a => [a] -> [a] uniq [] = [] uniq (x:xs) = x : filter (x/=) (uniq2 xs) Obviously a true 'unique' function has to traverse the entire list before it creates any output, as has been pointed out upthread. Phil -- http://www.kantaka.co.uk/ .oOo. public key: http://www.kantaka.co.uk/gpg.txt