Don't forget currying. Actually, in Haskell, function have exactly one argument. If you need more, just return a function. -- appears to have 2 arguments

Don't forget currying. Actually, in Haskell, function have exactly one argument. If you need more, just return a function. -- appears to have 2 arguments foo :: Int -> Int -> Int foo x y = x + (y * y) -- equivalent definition foo :: Int -> (Int -> Int) foo x = \y -> x + (y * y) -- or even more consistently foo :: Int -> (Int -> Int) foo = \x -> (\y -> x + (y * y)) Thinking this way is more useful in the long run: it makes partial application more natural. bar :: Int -> List Int -> List Int Bar = map (foo 42)