Usage and Examples

A whirlwind tour of Bnlang — every snippet here runs as-is with bnl <file>.bnl.

Hello, World

print("Hello, World!");

Run it:

bnl hello.bnl

Variables and basic types

Bnlang has one declaration keyword: var. Values are dynamically typed but predictable.

var name        = "Alice";
var age         = 25;
var is_admin    = true;
var nothing     = null;
var items       = [1, 2, 3];
var user        = { id: 1, name: "Alice" };

print(name, age, is_admin);
print("items:", items.length);
print("user id:", user.id);

Control flow

var score = 85;

if (score >= 80) {
    print("Grade: A+");
} else if (score >= 70) {
    print("Grade: A");
} else {
    print("Grade: below A");
}

Loops

// for ... of — iterate over a list
for (var n of [1, 2, 3, 4, 5]) {
    print(n);
}

// classic while
var i = 0;
while (i < 3) {
    print("tick", i);
    i = i + 1;
}

There is no for (i = 0; i < n; i++) C-style loop and no ++/--. Use for ... of over a list, or while for counter-driven loops. break and continue work in both.

Functions

function greet(name) {
    return "Hello, " + name + "!";
}

print(greet("Alice"));

Functions are fixed-arity — no defaults, no overloads, no varargs. Split into separately-named functions if you need different shapes.

Importing the standard library

import "io"   as io;
import "path" as path;

var text = io.read_file("notes.txt");
print("read", text.byte_length, "bytes from", path.basename("notes.txt"));

Async (callback-style)

There are no async/await keywords. Async I/O takes a final callback that fires when the work is done:

import "io" as io;

io.read_file_async("notes.txt", function (err, data) {
    if (err != null) {
        print("read failed:", err);
        return;
    }
    print("got", data.byte_length, "bytes");
});

print("scheduled");

For composing many async steps, use the async library:

import "async" as async;

async.parallel([
    function (cb) { io.read_file_async("a.txt", cb); },
    function (cb) { io.read_file_async("b.txt", cb); }
], function (err, results) {
    print("got", results.length, "files");
});

Error handling

function divide(a, b) {
    if (b == 0) { throw "divide by zero"; }
    return a / b;
}

try {
    print(divide(10, 0));
} catch (e) {
    print("caught:", e);
} finally {
    print("done");
}

A tiny web server

import "web" as web;

var app = web.app();
app.get("/", function (req) { return "Hello from Bnlang!"; });
app.get("/echo/:name", function (req) {
    return "Hi, " + req.params.name;
});
app.listen({ port: 3000 });

That's the language end-to-end. Browse the rest of the docs for module references and the keyword pages for syntax details.