Extensions

Extensions are a pattern for adding new functionality to Gleam modules. Consider Gleam's http client (gleam/http) as an example. We might want to implement additional setters on top of the Request type.

// project/extended/http_ext.gleam
import gleam/option.{type Option}
import gleam/http/request.{type Request}

pub fn set_query_string(
  request: Request(body),
  query: Option(String),
) -> Request(body) {
  Request(..request, query: query)
}

Using an extension module, it's easier to read and understand code that uses it. For example, here's