fun keyword

fun defines named functions and anonymous functions.

fun add_one(x: Int): Int {
  x + 1
}

test two_add_one {
  assert(add_one(2) == 3)
}

Type annotations are optional. A function without type annotations is assumed to take any type as an argument, and may return any type.

fun add_one(x) {
  x + 1
}

You can also use fun to declare anonymous functions, sometimes called lambdas.

let f = fun(x: Int): Int { 
  x + 1 
}
assert(f(2) == 3)