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Gleam is a friendly, statically typed functional language that compiles to Erlang (and JavaScript), running on the BEAM virtual machine. It brings a powerful type system with type inference, immutable data, and pattern matching to the Erlang ecosystem, letting developers build fault-tolerant, highly concurrent systems with compile-time guarantees. Gleam interoperates with existing Erlang and Elixir libraries, so it slots into the mature OTP world.
CompileBytes runs Gleam version 1.14.0. Gleam programs are organized into modules, use the `pub fn` syntax for public functions, and rely heavily on pipelines, the `case` expression for pattern matching, and custom types. The online environment is a quick way to explore Gleam's syntax and type system, see compiler error messages, and run small programs without installing the Gleam toolchain or an Erlang/OTP runtime locally.
main.gleam is the entry point for each run.
Use the Input panel to pipe standard input to your program when it needs data.
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import gleam/io
pub fn main() {
io.println("Hello, World!")
}import gleam/io
import gleam/int
pub fn double(x: Int) -> Int {
x * 2
}
pub fn main() {
4
|> double
|> int.to_string
|> io.println
}import gleam/io
import gleam/int
pub fn factorial(n: Int) -> Int {
case n {
0 -> 1
_ -> n * factorial(n - 1)
}
}
pub fn main() {
io.println(int.to_string(factorial(5)))
}import gleam/io
pub type Shape {
Circle(Float)
Square(Float)
}
pub fn describe(s: Shape) -> String {
case s {
Circle(_) -> "a circle"
Square(_) -> "a square"
}
}
pub fn main() {
io.println(describe(Circle(2.0)))
}import gleam/io
import gleam/int
import gleam/list
import gleam/string
pub fn main() {
[1, 2, 3, 4, 5]
|> list.map(fn(x) { x * x })
|> list.map(int.to_string)
|> string.join(", ")
|> io.println
}import gleam/io
import gleam/int
pub fn safe_divide(a: Int, b: Int) -> Result(Int, String) {
case b {
0 -> Error("divide by zero")
_ -> Ok(a / b)
}
}
pub fn main() {
case safe_divide(10, 2) {
Ok(value) -> io.println(int.to_string(value))
Error(msg) -> io.println(msg)
}
}import gleam/io
import gleam/int
import gleam/list
pub fn main() {
let total =
[1, 2, 3, 4, 5]
|> list.fold(0, fn(acc, x) { acc + x })
io.println(int.to_string(total))
}import gleam/io
import gleam/int
pub fn min_max(a: Int, b: Int) -> #(Int, Int) {
case a < b {
True -> #(a, b)
False -> #(b, a)
}
}
pub fn main() {
let #(lo, hi) = min_max(9, 3)
io.println(int.to_string(lo) <> " " <> int.to_string(hi))
}The editor uses Monaco, the engine behind VS Code, with language-aware editing tools and familiar keyboard controls.
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Gleam is one of 46 single-file compiler scratchpads. Each run submits only main.gleam; local sibling-file imports are not enabled.
Linked-project languages (23): Node.js, TypeScript, Deno, Python, C, Go, Dart, Swift, Rust, Ruby, PHP, Java, Kotlin, C++, C#, Nim, Crystal, Haxe, Zig, Scala, D, Bun, Objective-C.
Single-file scratchpads (46): Matplotlib, NumPy, pandas, Haskell, Clojure, Perl, Lua, Tcl, jq, Raku, Elixir, Bash, Zsh, Nushell, R, Assembly (NASM), Julia, Octave, Groovy, PowerShell, Visual Basic .NET, Odin, Pascal, Lisp, Erlang, CoffeeScript, COBOL, BASIC, V, Racket, OCaml, Prolog, AWK, Emacs Lisp, Emojicode, Forth, F#, Fortran, Assembly (NASM64), Solidity, Mojo, Ada, WASM (WAT), Gleam, Shell Script (sh), Scheme.
Download file exports the active Gleam source file.