Basics in

About Basics

Functions

In Gleam functions are defined using the pub fn syntax.

pub fn add(x: Int, y: Int) -> Int {
  x + y
}

This function takes two arguments, both of type Int, and returns a value of type Int. There is no return keyword in Gleam, the value of the last expression in a function is always implicitly returned.

The type annotations for arguments and the return type are optional, and Gleam will always fully type check your code. Typically Gleam programmers will give their functions type annotations for clarity, but you may omit them if you wish.

pub fn add(x, y) {
  x + y
}

A function can be called using the function_name(argument1, argument2) syntax.

pub fn double(x: Int) -> Int {
  // Call the add function defined above
  add(x, x)
}

Variables

In Gleam variables are defined using the let name = expression syntax.

pub fn main() {
  let count = 1
}

Variables can be declared with type annotations. Like function arguments these are optional, though most Gleam programmers will omit type annotations for variables.

pub fn main() {
  let count: Int = 1
}

String literals

In Gleam strings are written using double quotes.

pub fn greeting() {
  "Hello, world!"
}

Code comments

Comments can be used to leave notes for other developers reading the source code. Comments in Gleam are single lines preceeded by //.

pub fn main() {
  // This is a comment
  let x = 1
}