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 _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
