gistfile1.txt

perm ::  [Int] -> [ [Int]]
perm [] = return [] 
perm (x:xs) = do ys <- perm xs
                 zs <- insert x ys
                 return zs

insert ::  a -> [a] -> [[a]]
insert x xs = (return (x:xs))
              `mplus` case xs of 
                        []     -> mzero
                        (y:ys) -> liftM (y:) (insert  x ys)