Functions and Lambdas

Novum represents user-defined functions as lambda expressions. There is no separate required fn declaration syntax for ordinary functions.

Lambda syntax

Expression body:

square = |x| x * x

Block body:

compute = |x| {
    let y = x * 2
    y + 1
}

Multiple parameters:

add = |x, y| x + y

add(2, 3)

Named arguments work with user-defined lambdas/functions:

add(y=3, x=2)

Mixed calls are also supported as long as positional arguments come first:

add(2, y=3)

Unknown parameter names are errors.
Supplying one parameter more than once is an error.
Positional arguments after a named argument are errors.
Missing required parameters are errors.
self is injected automatically for bound methods and cannot be supplied explicitly as a named argument.

Because functions are values, they can be passed to iterator methods:

[1, 2, 3]
    .map(|x| x * 2)
    .collect()

A lambda bound to a name can refer to that name recursively when the environment semantics permit it:

factorial = |n| {
    if n <= 1 {
        1
    } else {
        n * factorial(n - 1)
    }
}