module Composition where
    -- Haskell doesn't have a simple "subclass of Object" generic (https://stackoverflow.com/questions/6479444/is-there-a-type-any-in-haskell) but you can just use arbitrary values and not bind them to anything!
    -- The code in the book does this in the CLI and just avoids the signature definition
    second :: [o] -> o
    -- Here we use an implicit argument (so just the function to the left) which then becomes an implicit parameter to tail, which has head invokes on it due to function composition by "." (https://wiki.haskell.org/Function_composition)
    second = head . tail

    -- Fibonacci - like in fibonacci.hs, but without the index
    fib :: Integer -> Integer
    fib = fst . fibNthPair
    
    fibNextPair :: (Integer, Integer) -> (Integer, Integer)
    fibNextPair (x, y) = (y, x + y)

    fibNthPair :: Integer -> (Integer, Integer)
    fibNthPair 1 = (1, 1)
    fibNthPair n = fibNextPair (fibNthPair (n - 1))