Functions

lil has two kinds of functions: built-in library functions from the standard libraries, and user-defined functions you write yourself.

Built-in Library Functions

These are functions that come with lil, organized by library like math, string, file, sys, and date. You call them with func(args)@lib syntax:

randint@math(1, 6)

The function name comes first, then @, then the library name, then arguments in parentheses.

name = "alice"
upper@string(name)
write(name)

See the Built-in Libraries page for the full list of available functions.

User-defined Functions

When you need custom logic, define your own functions with # syntax:

#add(a, b) {
  a + b
}

There’s no def, no colon, and no return keyword. The function body is a block in braces, and the last expression’s value is automatically returned.

result = add(3, 4)
write(result)

Functions can also be created without a name (anonymous functions/closures) for inline use:

double = #(x) { x * 2 }
write(double(5))

See User-defined Functions and Advanced Functions for details.

Choosing Which to Use

Library functions handle built-in operations: math, strings, files, dates, system commands. User-defined functions let you organize your own code, avoid repetition, and build reusable abstractions. You’ll typically use both together.