-- module.hs

module MyModule where

once :: (a -> a) -> (a -> a)
once = \x -> x

twice :: (a -> a) -> (a -> a)
twice f x = f (f x)

thrice :: (a -> a) -> (a -> a)
thrice f x = f (f (f x))

four_times :: (a -> a) -> (a -> a)
four_times f = twice (twice f)



-- ch4.hs

module Chapter4 where
import MyModule

minus2 :: Num a => a -> a
minus2 x = x-2

minus6 = thrice minus2

plus3 :: Num a => a -> a
plus3 = (+3)

same :: Num a => a -> a
same = minus6.plus3.plus3