Code that says
what it means.
Pleno is a readable, dynamically typed language with optional checked types, classes and pattern matching, async built in, and the tools to go with it.
curl -fsSL https://raw.githubusercontent.com/otabekoff/pleno/main/scripts/install.sh | shenum Shape { Circle(radius), Rect(width, height)} fn area(shape: Shape): Float { match (shape) { case Shape.Circle(r) => return 3.14159 * r * r, case Shape.Rect(w, h) => return w * h }} let shapes = [Shape.Circle(2.0), Shape.Rect(3.0, 4.5)];for (shape in shapes) { print(`${shape}: ${area(shape)}`);}The language at a glance
Familiar syntax, with the parts you would expect from a modern language.
Types when you want them
Leave them out, or annotate parameters, fields and results. Annotations are checked when the code runs.
fn area(w: Float, h: Float): Float { return w * h;} let maybe: Int? = null;let id: Int | String = "user-42";Classes that keep secrets
Private fields are really private, and interfaces are checked.
class Counter { private count: Int = 0; fn next(): Int { this.count += 1; return this.count; }}Enums and pattern matching
Enums carry data, and match takes them apart with guards and bindings.
let label = match (status) { case Status.Ok => "done", case Status.Failed(why) => why, case _ => "waiting"};Async built in
async and await, spawn, channels and mutexes, on an event loop.
import { Channel } from "std:concurrency"; let jobs = Channel(8);spawn(fn() { jobs.send("build"); jobs.close();});for (job in jobs) { print(job); }Pipelines and closures
Data flows left to right, and functions are values.
let squares = 1..=10 |> filter(fn(n) => n % 2 == 0) |> map(fn(n) => n * n);Tests in the box
describe, test and assert come with the language; pleno test runs them.
import { test, assert } from "std:test"; test("adds", fn() { assert.equal(1 + 1, 2);});A standard library that covers the basics
Files, processes, HTTP, data formats, regular expressions, time, crypto and tests.
All modulesOne toolchain
pleno runs, checks, formats, lints and tests. plm creates projects and manages dependencies. pleno-lsp and pleno-dap power the VS Code extension, which can install all of them for you.
$ plm init my-app Pleno created my-app ✔ pleno.toml ✔ src/main.pln ✔ tests/integration_test.pln $ plm test math ✓ adds numbers ✓ compares numbers PASSED $ pleno check src/main.pln src/main.pln:3:5: error: undefined variable 'prnt'
Where Pleno is
Pleno is at 0.2. It runs real programs today; the plan for 1.0 lists what is left.
Works today
- Gradual types, classes, enums, generics
- async and await, channels, mutexes
- A standard library of 25 modules
- Formatter, linter, tests, language server, debugger
Before 1.0
- A frozen language specification
- Faster execution
- Destructuring and one error shape
- Signed releases in package managers
After 1.0
- A JIT compiler
- A generational garbage collector
- A public package registry
- A self-hosted compiler
Learn Pleno in an afternoon
Fifteen short lessons, each with code you can edit and run in the page.
Start the tutorial