script.foo

-- Foo Lang 
-- Script below containts valid code.

-- Identity function with polymorphic type
let identity x = x
-- Equivalent to expression below using lambda
let identity = (\x -> x)

-- a few polymorphic functions

-- Returns first argument
let fst a b = a

-- Returns second argument
let snd a b = b

-- Classic haskell function
let flip f x y = f y x

-- Functions returing the same output regardless of input
let constOne = fst 1

let constTrue = fst True

-- Absolute value of an integer
let abs x = 
    if (x < 0) then
        (-1) * x
    else
        identity x

-- To create recursive functions add rec keyword after let.
let rec fib n = 
    if (n <= 0) then 
        0
    else if (n == 1) then 
        1
    else 
        (fib (n - 1)) + (fib (n - 2)) 


-- This is somewhat untrue definiton of a factorial function,
-- but let's not worry about gamma function and fancy math definitions :)
let rec factorial n = 
    if (n <= 1) then 
        1
    else
        n * (factorial (n - 1))