On Thursday 12 July 2007, Dan Weston wrote:
Now that I mention it, the base case is much less often called than the recursive case, so I would in hindsight flip the order of the two (mutually exclusive) partial function definitions:
unique :: Eq a => [a] -> [a] unique (x:xs) = x : (unique . filter (/= x) $ xs) unique [] = []
This should be marginally more efficient. I doubt that GHC would automatically detect that a) they are mutually exclusive and b) the second is called less often than the first!
Actually, it would (well, sort of). GHC expends a good deal of effort looking for cases where pattern-matching is mutually-exclusive, and flattens it out to unique xn' = case xn' of [] -> [] x : xn -> x : unique (filter (/= x) xn) where each branch is equally efficient. Jonathan Cast http://sourceforge.net/projects/fid-core http://sourceforge.net/projects/fid-emacs