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About Options

The Option type is used to represent values that can either be absent or present.

It is defined in the gleam/option module as follows:

type Option(a) {
  Some(a)
  None
}

The Some constructor is used to wrap a value when it's present, and the None constructor is used to represent the absence of a value.

Accessing the content of a Option is often done via pattern matching.

import gleam/option.{type Option, None, Some}

pub fn say_hello(person: Option(String)) -> String {
  case person {
    Some(name) -> "Hello, " <> name <> "!"
    None -> "Hello, Friend!"
  }
}

say_hello(Some("Matthieu"))
// -> "Hello, Matthieu!"

say_hello(None)
// -> "Hello, Friend!"

The gleam/option module also defines a number of useful function for working with Option types, such as unwrap, which returns the content of an Option or a default value if it is None.

import gleam/option.{type Option}

pub fn say_hello_again(person: Option(String)) -> String {
  let name = option.unwrap(person, "Friend")
  "Hello, " <> name <> "!"
}