Gleam (programming language)

Gleam is a general-purpose, concurrent, functional high-level programming language that compiles to Erlang or JavaScript source code.^[2][7][8]

Gleam

Lucy, the starfish mascot for Gleam[1]
Paradigm	Multi-paradigm: functional, concurrent[2]
Designed by	Louis Pilfold
Developer	Louis Pilfold
First appeared	June 13, 2016; 8 years ago (2016-06-13)
Stable release	1.10.0[3]  / 14 April 2025
Typing discipline	Type-safe, static, inferred[2]
Memory management	Garbage collected
Implementation language	Rust
OS	FreeBSD, Linux, macOS, OpenBSD, Windows[4]
License	Apache License 2.0[5]
Filename extensions	.gleam
Website	gleam.run
Influenced by
Alpaca Elm Erlang Elixir Go JavaScript OCaml Rust [6]

Gleam is a statically-typed language,^[9] which is different from the most popular languages that run on Erlang’s virtual machine BEAM, Erlang and Elixir. Gleam has its own type-safe implementation of OTP, Erlang's actor framework.^[10] Packages are provided using the Hex package manager, and an index for finding packages written for Gleam is available.^[11]

History

The first numbered version of Gleam was released on April 15, 2019.^[12] Compiling to JavaScript was introduced with version v0.16.^[13]

In 2023 the Erlang Ecosystem Foundation funded the creation of a course for learning Gleam on the learning platform Exercism.^[14]

Version v1.0.0 was released on March 4, 2024.^[15]

Features

Gleam includes the following features, many common to other functional programming languages:^[8]

• Result type for error handling
• Immutable objects
• Algebraic data types
• Pattern matching
• No null pointers
• No implicit type conversions

Example

A "Hello, World!" example:

import gleam/io

pub fn main() {
  io.println("hello, world!")
}

Gleam supports tail call optimization:^[16]

pub fn factorial(x: Int) -> Int {
  // The public function calls the private tail recursive function
  factorial_loop(x, 1)
}

fn factorial_loop(x: Int, accumulator: Int) -> Int {
  case x {
    1 -> accumulator

    // The last thing this function does is call itself
    _ -> factorial_loop(x - 1, accumulator * x)
  }
}

Implementation

Gleam's toolchain is implemented in the Rust programming language.^[17] The toolchain is a single native binary executable which contains the compiler, build tool, package manager, source code formatter, and language server. A WebAssembly binary containing the Gleam compiler is also available, enabling Gleam code to be compiled within a web browser.