Functions

Defining Functions

Functions in Gleam are declared with the fn keyword:

fn add(a: Int, b: Int) -> Int {
  a + b
}

The last expression in a function body is automatically returned. There is no return keyword.

Public Functions

By default, functions are private to their module. Use pub to make them accessible from other modules:

pub fn greet(name: String) -> String {
  "Hello, " <> name <> "!"
}

Labeled Arguments

Gleam supports labeled arguments, which make function calls more readable:

pub fn replace(
  in string: String,
  each pattern: String,
  with replacement: String,
) -> String {
  // ...
}

// Called with labels:
replace(in: "hello world", each: "world", with: "gleam")

The label comes before the parameter name. At the call site, you use the label.

Anonymous Functions

You can create functions without names:

let double = fn(x: Int) -> Int { x * 2 }
double(5)  // 10

Anonymous functions are commonly used with higher-order functions like list.map.

Multiple Expressions

A function body can contain multiple expressions. Each expression except the last is evaluated for its side effects:

pub fn main() {
  io.println("first")
  io.println("second")
  io.println("third")
}

Your Task

Write a function called greet that takes a name and returns a greeting in the format Hello, <name>!. Use it in main to greet "World" and "Gleam" on separate lines.