Gleam programming language

Installing Erlang

Since Gleam primarily compiles to Erlang (with optional JavaScript support), you’ll need Erlang installed on your system first.

On Linux and macOS:

• Homebrew (macOS): brew install erlang
• MacPorts (macOS): port install erlang
• Ubuntu/Debian: apt-get install erlang
• Fedora: yum install erlang
• Arch Linux/Manjaro: pacman -S erlang
• FreeBSD: pkg install erlang

On Windows: Download and install Erlang using the official installers:

• 64-bit
• 32-bit

Installing Gleam

The simplest way to get Gleam is from the GitHub releases page. Download the latest release for your operating system and follow the installation instructions.

Building from Source

You may want to build Gleam from source if you’re contributing to the language or compiling it for WebAssembly.

1. Clone the repository:

   git clone https://github.com/gleam-lang/gleam
   cd gleam
   

2. Install Rust: Gleam’s compiler is written in Rust. Install it via rustup:

   • Linux/macOS:

     curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
     

   • Windows: Download the installer from the Rust website, run it, then use:

     rustup toolchain install stable
     

3. Build the compiler:

   cargo install --path gleam-bin 
   

   This installs Gleam globally on your system.

Building for WebAssembly

To compile Gleam for WebAssembly, install wasm-pack:

• Linux/macOS:

  curl https://rustwasm.github.io/wasm-pack/installer/init.sh -sSf | sh
  

• Windows (alternative):

  cargo install wasm-pack
  

Then build the WebAssembly target:

cd compiler-wasm
wasm-pack build --target web

Hello world

Let us now write our first Gleam program! If you don’t have Gleam installed, it is recommended to follow instructions in the previous section. Run:

gleam new hello_world
cd hello_world

You can now see the automatically generated Gleam project structure:

hello_world
|_ .github/workflows
   |_ test.yml
|_ src
   |_ hello_world.gleam
|_ test
   |_ hello_world_test.gleam
|_ .gitignore
|_ gleam.toml
|_ README.md

The entry point is located in the src/hello_world.gleam file. It will probably look something like this:

import gleam/io

pub fn main() {
  io.println("Hello from hello_world!")
}

Let us change our program, so that it prints canonical Hello, world! message:

import gleam/io

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

As you can see, Gleam doesn’t require semicolons. To run the program, you can use gleam run command:

$ gleam run
  Compiling gleam_stdlib
  Compiling gleeunit
  Compiling hello_world
   Compiled in 1.78s
    Running hello_world.main
Hello, world!

By default, it transpiles our code to erlang and uses it to run our code. However, you can also use javascript using --target flag:

$ gleam run --target javascript
  Compiling gleam_stdlib
  Compiling gleeunit
  Compiling hello_world
   Compiled in 1.5s
    Running hello_world.main
Hello, world!

You can also use specific javascript runtime using --runtime flag:

$ gleam run --target javascript --runtime node
  Compiling gleam_stdlib
  Compiling gleeunit
  Compiling hello_world
   Compiled in 1.5s
    Running hello_world.main
Hello, world!