* Kazu Yamamoto
Hello,
My friend reached the following version:
chop :: String -> String chop = foldr go [] where go x xs | isSpace x && null xs = [] | otherwise = x:xs
This version is faster than the reverse version in most cases. The point is checking "isSpace" first and falling into "otherwise" in many cases, which is a natural co-recursion.
This was exactly my first attempt on rewriting your foldr version. Unfortunately, it doesn't seem faster at all (foldr2 below). The test input was replicate 100 'a' ++ replicate 100 ' '. GHC 7, -O2. benchmarking all/foldr mean: 2.808462 us, lb 2.807047 us, ub 2.810520 us, ci 0.950 std dev: 8.620822 ns, lb 6.535738 ns, ub 11.59552 ns, ci 0.950 benchmarking all/reverse mean: 4.128217 us, lb 4.125409 us, ub 4.134086 us, ci 0.950 std dev: 20.07591 ns, lb 11.47572 ns, ub 38.33738 ns, ci 0.950 benchmarking all/foldr2 mean: 6.701714 us, lb 6.692093 us, ub 6.711627 us, ci 0.950 std dev: 50.06638 ns, lb 42.25004 ns, ub 64.84223 ns, ci 0.950 -- Roman I. Cheplyaka :: http://ro-che.info/