roc-stuff/higher-order.roc

app "higher-order"
    packages { pf: "https://github.com/roc-lang/basic-cli/releases/download/0.7.1/Icc3xJoIixF3hCcfXrDwLCu4wQHtNdPyoJkEbkgIElA.tar.br" }
    imports [pf.Stdout, pf.Task]
    provides [main] to pf

main : Task.Task {} I32
main =
    fn1 = bind Num.sub 3
    fn2 = bindL Num.mul 3
    fn3 = compose fn1 fn2
    fn4 = compose fn2 fn1
    fn5 = compose (compose fn1 fn2) (compose fn3 fn4)
    fn6 : F64 -> Int a
    fn6 =
        (\n -> n)
        |> compose Num.sqrt
        |> compose Num.ceiling
    results =
        [fn1 2, fn2 2, fn3 2, fn4 2, fn5 2, fn6 9]
        |> List.map Num.toStr
        |> List.mapWithIndex \e, idx -> "fn$(Num.toStr idx) -> $(e)"
        |> Str.joinWith "\n"
    Stdout.line "$(results)"

bind : (a, b -> c), a -> (b -> c)
bind = \fn, a ->
    \b -> fn a b

bindL : (a, b -> c), b -> (a -> c)
bindL = \fn, b ->
    \a -> fn a b

compose : (a -> b), (b -> c) -> (a -> c)
compose = \fn1, fn2 ->
    \a -> fn1 a |> fn2