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Ints

There are two different kinds of numbers in Gleam - ints and floats.

Ints are whole numbers.

let integer = 3
// -> 3

Gleam has several operators that work with ints.

1 + 1 // -> 2
5 - 1 // -> 4
5 / 2 // -> 2
3 * 3 // -> 9
5 % 2 // -> 1

2 > 1  // -> True
2 < 1  // -> False
2 >= 1 // -> True
2 <= 1 // -> False

Floats

Floats are numbers with one or more digits behind the decimal separator.

let float = 3.45
// -> 3.45

Floats also have their own set of operators.

1.0 +. 1.4 // -> 2.4
5.0 -. 1.5 // -> 3.5
5.0 /. 2.0 // -> 2.5
3.0 *. 3.1 // -> 9.3

2.0 >. 1.0  // -> True
2.0 <. 1.0  // -> False
2.0 >=. 1.0 // -> True
2.0 <=. 1.0 // -> False

Modules

Modules

Gleam code is organised into modules, and each file is one Gleam module.

Up until now we have written functions with the pub fn syntax, which defines a function that is publicly available to other modules. Functions defined with fn are private to the module they are defined in and cannot be used by other modules.

// This function is public
pub fn add(x, y) {
  x + y
}

// This function is private
fn subtract(x, y) {
  x - y
}

Gleam modules have names, and the name is based on their file path within the src or test directory.

For example, a module defined in src\geometry\rectangle.gleam (on Windows) or src/geometry/rectangle.gleam (on UNIX-like operating systems) would be named geometry/rectangle.

Importing functions from other modules

Accessing functions defined in other modules is done via imports. All functions within that module that were exposed by it are made accessible when importing that module. But how they are accessed varies depending on how the module is imported.

Qualified imports are the default, and accessing a function within such module (for example the map function in the gleam/list module) is done by prefixing the module name (list.map).

// Import the int module
import gleam/int

pub fn run(x: Int) -> String {
  // Use the to_string function from the int module
  int.to_string(x)
}

By default the name used to refer to the module is the last part of the module name, in this case int, but this can be changed by using the as keyword.

// Import the int module and refer to it as i
import gleam/int as i

pub fn run(x: Int) -> String {
  i.to_string(x)
}

Unqualified imports enable direct access to the exposed functions within that module, without prefixing.

// Import the to_string function from the int module
import gleam/int.{to_string}

pub fn run(x: Int) -> String {
  to_string(x)
}

Qualified imports are preferred as they make it clearer to the reader where a function comes from, and to avoid name clashes.

Standard library

Gleam has a rich and well-documented standard library. The documentation is available online at hexdocs.pm/gleam_stdlib. Save this link somewhere - you will use it a lot!

Most built-in data types have a corresponding module that offers functions for working with that data type, e.g. there's the gleam/int module for ints, gleam/string module for strings, gleam/list module for lists and so on.