This repository contains source code for Riff's standalone online playground. The playground is 100% client-side, using a special Riff interpreter compiled to WebAssembly to execute Riff programs directly in the browser.

Usage

To run the playground locally, you'll need to to spin up a local web server to serve index.html. Otherwise, the Riff interpreter (WebAssembly module) cannot be invoked via the file:// protocol.

Example

Start a local server on port 8000 using Python:

$ python3 -m http.server 8000

You can then open localhost:8000 in a new browser tab/window.

How it Works

Emscripten is used to compile the Riff interpreter to WebAssembly. Emscripten is used since it takes care of linking any required headers/libraries to the WASM module.

The following command is used to compile the C source code:

$ emcc -O3 *.c -s EXPORTED_FUNCTIONS='["_wasm_main"]' -s EXPORTED_RUNTIME_METHODS='["ccall"]' -o riff.js

Emscripten outputs a JavaScript file along with the WASM module, which is used to drive the WASM module.

wasm_main() is a special entry point which simply skips any command-line argument parsing. Note that this was done to simplify invocation from JavaScript and isn't really necessary.

The Riff interpreter is invoked via JavaScript via Emscripten's provided Module interface:

// Grab the input program from the CodeMirror "input" area
var inputProgram = cmInput.getValue();

// Invoke Riff with the input program
// 0 = Disassemble
// 1 = Execute
Module.ccall('wasm_main', 'number', ['number', 'string'], [1, inputProgram]);

Printing to stdout and stderr is defined through Emscripten's Module object. In this example, both stdout and stderr are appended to an HTML <textarea> with the ID #output:

var Module = {
    // stdout
    print: function(text) {
        console.log(text);
        document.getElementById('output').value += text + "\n";
    },

    // stderr
    printErr: function(text) {
        console.error(text);
        document.getElementById('output').value += text + "\n";
    },
};