beni

A complete app

A counter with two buttons.

type alias Model =model{ "count": 0 }
    count : Int


type Msg
    = Inc
    | Dec


update : Msg, Model → Model
update msg model =
    case msg of
        Inc →
            { model | count = model.count + 1 }

        Dec →
            { model | count = model.count - 1 }


view : Model → Html Msg
view model =
    ?built-in JSX compiler<div>
    <button onClick={Dec}>-</button>
    <output>{model.count}</output>
    <button onClick={Inc}>+</button>
</div>


main : Tea.Program
main = Tea.sandbox { init = λ⊤ → { count = 0 }, update = update, view = view }

1 / 4

Compiled to vanilla JavaScript

beni's compiler turns your program into what carefully hand-tuned vanilla JavaScript would look like. The output is fast and small.

beni ships a minimal runtime, and each component adds very little to the bundle, so the app stays small as it grows.

The counter above compiles to 419 bytes after compression.

2 / 4

Immutability

Values are immutable, but a List is a plain JavaScript array. When nothing reads the old list, the compiler edits it in place. When something does, the program doesn’t compile, and the message shows the fix.

after = List.push (List.copy xs) 0

The ownership rules are being proved in Lean.

3 / 4

Effects

The compiler infers which functions can wait on a file, the network or a timer. Those run on beni’s fiber runtime, the rest compile to plain JavaScript functions. There is no async or await in the source.

size path =
    case Io.readFile path of
        Ok text → String.length text
        Err _ → 0

The fiber runtime is only included when a program can wait.

4 / 4

Validation

A schema describes your data, and the compiler turns it into a parser for exactly that shape. No validation library is shipped. A failure is a list of issues, never an exception.

schema User =
    name : String
    email : String
    age : Int optional

main =
    case User.parse text of
        Ok user → Node.print user.name
        Err issues → Node.printLines (List.map issues describe)

const name = value.name;
if (name === undefined) return fail("name", "missing key \"name\"");
if (typeof name !== "string") return fail("name", "expected a string");
const email = value.email;
...
return { name, email, age };

The same schema also gives a printer, User.print, that writes the value back to JSON.

Output size

A build contains only the code its program uses.

419 B

The counter above

985 B

Validate a User and report its issues

2.2 kB

Read a file, parse it, print a field (includes the fiber runtime)

Size after brotli

Guarantees

• No runtime exceptions.
• Every case handles every possibility.
• Every failure of a host API comes back as a typed value.
• When the compiler refuses a program, the message names the problem and a fix.

Platforms

Browser · Node · Cloudflare Workers

The compiler

• Written in Zig.
• Files are parsed in parallel, and modules are checked in parallel along their dependencies.
• Rebuilds are incremental.
• The output is the same byte for byte, whatever the number of threads.
• The same compiler runs in the browser as WebAssembly. The playground uses it.

Research