sgleam

sgleam is a version of Gleam for students. It has a REPL, runs a single .gleam file without a project, and comes with libraries for drawing images and writing interactive programs, in the spirit of HtDP.

You can try it in the browser at https://malbarbo.pro.br/sgleam/. The web version has an editor, the REPL, and shows images and interactive programs inline.

sgleam uses the Gleam compiler and runs the generated JavaScript on QuickJS, through rquickjs. There is a similar project for Python, spython.

Install

Download the archive for your system from the releases page, extract it, and put the sgleam binary somewhere on your PATH. That is all. The Gleam standard library ships inside the binary.

To build from source you need stable Rust:

cargo build --release

Use

sgleam with no arguments starts the REPL. It highlights the code as you type, completes names with tab, and keeps reading when an expression is not finished.

To run a program, give it the file:

sgleam hello.gleam

sgleam calls the main function of the file. A program that reads from stdin defines smain instead, and gets the input as one String or as a List(String) of lines:

import gleam/io
import gleam/list
import gleam/string

pub fn smain(lines: List(String)) {
  lines
  |> list.map(string.reverse)
  |> list.each(io.println)
}

$ printf 'hello\nworld\n' | sgleam reverse.gleam
olleh
dlrow

Integers have arbitrary precision. The -n flag uses JavaScript numbers instead, which is faster.

Tests are functions whose names end in _examples. They state what a function returns for a few inputs, with the sgleam/check module, and sgleam test runs them:

import sgleam/check

pub fn double(x: Int) -> Int {
  x * 2
}

pub fn double_examples() {
  check.eq(double(0), 0)
  check.eq(double(3), 6)
}

sgleam format formats a file, and sgleam repl file.gleam loads the definitions of a file into the REPL. sgleam --help lists the rest.

Images and interactive programs

The sgleam/image module builds a picture out of shapes, places pictures over, beside, and above each other, and rotates, scales, and crops them. A picture is an SVG.

import sgleam/fill
import sgleam/image
import sgleam/stroke

image.overlay(image.circle(30, stroke.red), image.rectangle(80, 50, fill.blue))

The sgleam/world module is for animations and games. A program is a state, a function that draws the state, and functions that update the state on each tick of the clock or key press:

world.create(initial_state, draw)
|> world.on_tick(tick)
|> world.on_key_press(key)
|> world.run()

Both work best in the web version, which shows the picture as you go. The examples directory has a few complete programs.

Documentation

The guides are in English and in Portuguese. There is one for the command line and one for the web version, which also covers images and interactive programs.

Development

The workspace has three crates. engine has the compiler integration, the QuickJS runtime, and the REPL. cli is the binary, and wasm is the build for the browser.

make check      # clippy, cargo fmt, deno fmt
make test       # cargo test and the WASM tests
make test-rs    # cargo test only
make wasm       # the WASM binary

License

Apache 2.0. See LICENSE.