Currying

Functions can be curried, For example:

let
    link "listutils.fn" as list;

    fn mul(x, y) {
        x * y
    }
in
    list.map(mul(2), [1, 2, 3, 4]); // [2, 4, 6, 8]

Note that mul is defined with two arguments but called with only one, resulting in a closure that accepts the second argument and performs the computation. That closure is what gets handed to map which applies it to each element of the list.

Over-application (extra arguments)

In addition to partial application, you can also pass more arguments than a function’s declared arity. Extra arguments are applied one-by-one to the result of the call, left-to-right, as long as that result is itself a function.

Examples:

let f = fn (x, y) { fn (z) { x + y + z } };
in f(1, 2, 3)  // 6

Here f takes two arguments and returns a function. Calling f(1,2,3) applies (1,2) first, producing a new function, then applies the extra 3 to that result.

You can chain and nest multiple argument functions arbitrarily:

let g = fn (a, b) { fn (c, d) { fn (e) { a + b + c + d + e } } };
in g(1, 2, 3, 4, 5)  // 15

Next: Pattern Matching