Records

Records

Records in Gleam are custom types with a single variant that has labeled fields:

pub type Person {
  Person(name: String, age: Int)
}

The type name and constructor name are the same. You create a record by calling the constructor:

let alice = Person(name: "Alice", age: 30)

Accessing Fields

You can access fields with dot notation:

alice.name  // "Alice"
alice.age   // 30

Updating Records

Since all data is immutable, you create new records with updated fields using the spread syntax:

let older_alice = Person(..alice, age: alice.age + 1)

The ..alice copies all fields from alice, then age: alice.age + 1 overrides the age.

Pattern Matching on Records

You can destructure records in case expressions and let bindings:

let Person(name: name, age: age) = alice
// name = "Alice", age = 30

case person {
  Person(name: "Admin", ..) -> "admin user"
  Person(name: name, age: age) if age >= 18 -> name <> " is an adult"
  Person(name: name, ..) -> name <> " is a minor"
}

Records with Multiple Variants

A custom type can have multiple variants, each with their own fields:

pub type Animal {
  Dog(name: String, breed: String)
  Cat(name: String, indoor: Bool)
  Fish(name: String, species: String)
}

Your Task

Define a Rectangle record type with width and height fields (both Int). Write a function area that calculates the area, and a function describe that returns a string in the format "<width>x<height> (area: <area>)". Print descriptions for two rectangles.