sgleam

A student-friendly Gleam environment with an interactive REPL, image support, and interactive programs, designed for teaching functional programming.

sgleam is built on Gleam for compilation and QuickJS (via rquickjs) for execution. A similar project for Python is spython.

Features

• Gleam stdlib included — 18 standard library modules available out-of-the-box, no project setup required
• Scripting — run single .gleam files directly, without creating a Gleam project. Use smain to read from stdin, making sgleam suitable for solving Advent of Code challenges and other scripting tasks
• Interactive REPL — auto-indent, tab completion, multiline editing
• BigInt / Number modes — BigInt (default) for arbitrary-precision integers, or Number mode (-n) for better performance
• Image library — built-in SVG-based graphics library for teaching, inspired by HtDP image teachpacks
• Interactive programs — world library for animations and keyboard-driven programs
• Testing — check library for example-based testing
• WASM support — runs in the browser via a WASM build

Build

Requires Rust (stable). Dependencies are fetched automatically.

cargo build                # debug build
cargo build --release      # optimized build

Usage

# Start the REPL
sgleam

# Run a script
sgleam file.gleam

# Run with Number mode (instead of BigInt)
sgleam -n file.gleam

Scripting with smain

sgleam can run single .gleam files without a project. Define a smain function to read input from stdin:

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

/// Reads lines from stdin and prints them reversed
pub fn smain(lines: List(String)) {
  lines
  |> list.map(string.reverse)
  |> list.each(io.println)
}

echo -e "hello\nworld" | sgleam file.gleam
# olleh
# dlrow

The smain function accepts three signatures:

• fn smain() -> a — no input
• fn smain(input: String) -> a — all stdin as a single string
• fn smain(lines: List(String)) -> a — stdin split into lines

Image Library

sgleam includes a built-in image library for teaching graphics programming, inspired by the HtDP image teachpacks. Images are rendered as SVG.

import sgleam/image.{circle, overlay, rectangle, to_svg}
import sgleam/fill
import sgleam/stroke

let img = overlay(circle(30, stroke.red), rectangle(80, 50, fill.blue))

The library provides:

• Shapes — rectangles, circles, ellipses, triangles (7 constructors), polygons, stars, lines, wedges, bezier curves
• Transformations — rotate, scale, flip, crop
• Composition — overlay, underlay, beside, above (with alignment options)
• Scenes — place images at coordinates, draw lines/polygons/curves
• Text and fonts — text rendering with customizable fonts
• Styles — fill and stroke with color, opacity, width, dash patterns
• Colors — 140+ CSS named colors, rgb(), rgba()
• Animation — world library for interactive programs with keyboard input

Architecture

The workspace has three crates:

• engine — shared library (REPL engine, Gleam compiler integration, QuickJS runtime)
• cli — CLI binary with REPL
• wasm — WASM target for browser use

Development

make check              # clippy + fmt + deno fmt
make test               # cargo test + deno test (WASM)
make test-rs            # cargo test only (faster)
make wasm               # build WASM binary

License

Apache 2.0 — see LICENSE.