pointfree.hs

import Data.Char (toUpper)

-- space is high priority function application:
--     f x = f(x) in other languages

-- functions are defined like this:
--     f x = x * 2
-- is equivalent to
--     def f(x): return x * 2

-- to say f is SomeType:
--     f :: SomeType

-- $ is low priority function application:
--     f (g (h x))) = f $ g $ h x

-- IO () means "An IO action that doesn't return anything"
main :: IO ()
main = putStrLn $ reverseCapitalize "asdf qwerty zxcv" -- prints Zxcv Qwerty Asdf

-- pointfree
reverseCapitalize :: String -> String
reverseCapitalize = unwords . reverse . map capitalize . words

-- pointful
reverseCapitalize' :: String -> String
reverseCapitalize' s = unwords $ reverse $ map capitalize $ words s

-- you can define piecewise functions
--     f 1 = "One"
--     f 2 = "Two"
--     f x = "Anything else"
-- and pattern match on arguments, like how python lets you do
--     x, y = [1, 2]
capitalize :: String -> String
capitalize "" = ""
capitalize (first:rest) = toUpper first : rest
-- : is the list prepend operator
--     0:[1] = [0, 1]


-- in general
--     f x = blahBlah x
-- reduces to
--     f = blahBlah
-- see also https://wiki.haskell.org/Pointfree