swipl-wasm

SWI-Prolog WebAssembly build as a NPM package. Please see this page for ongoing progress and information: https://swi-prolog.discourse.group/t/swi-prolog-in-the-browser-using-wasm/5650

Quickly Getting Started

The easiest way to get started is my importing swipl-wasm into your npm project. It imported for both node and browser builds as follows:

script.mjs

import SWIPL from "swipl-wasm";

async function main() {
  const swipl = await SWIPL({ arguments: ["-q"] });
  console.log(swipl.prolog.query("member(X, [a, b, c]).").once().X);
}

main();

For those who have not done this before you will first need to install node and npm. After doing this you can make a new project as follows:

# Make the project directory
mkdir my-swipl-project && cd ./my-swipl-project
# Initialise the project
npm init
# Install swipl-wasm
npm i swipl-wasm

After this place the above code in script.mjs in the root of your directory and run node script.mjs to run the script.

Usage

In browser:

<div id="solution"></div>
<script src="/dist/swipl/swipl-web.js"></script>
<script>
  (async () => {
    const swipl = await SWIPL({
      arguments: ["-q"],
      locateFile: (path) => {
        return `/dist/swipl/${path}`;
      },
    });
    const query = "member(X, [a, b, c]).";
    const solutionElement = document.getElementById("solution");
    const firstSolution = swipl.prolog.query(query).once().X;
    solutionElement.textContent = firstSolution;
  })();
</script>

The function locateFile will help the browser to find the necessary files (swipl-web.wasm and swipl-web.data). In this case the files should be served along with swipl-web.js under the /dist/swipl directory in the web server.

You can run this example by executing npm run test:serve-http and visiting http://localhost:8080/examples/browser.html.

In Nodejs:

const SWIPL = require("swipl-wasm");

const swipl = await SWIPL({ arguments: ["-q"] });
console.log(swipl.prolog.query("member(X, [a, b, c]).").once().X);

You can run this example with node examples/run-on-node.js.

Using single-file bundle

The swipl-wasm package comes also with the single-file bundle. This does not require distributing the .data and .wasm files which are now embedded into the .js file instead.

<div id="solution"></div>
<script src="/dist/swipl/swipl-bundle.js"></script>
<script>
  (async () => {
    const swipl = await SWIPL({ arguments: ["-q"] });
    const query = "member(X, [a, b, c]).";
    const solutionElement = document.getElementById("solution");
    const firstSolution = swipl.prolog.query(query).once().X;
    solutionElement.textContent = firstSolution;
  })();
</script>

Generating an image

Often you will want to bundle a pre-built image of your Prolog file. The easiest way to do this is using the swipl-generate command to generate the image. For example in ./examples/generation the script: swipl-generate ./max.pl ./dist/max.ts will generate a file ./dist/max.ts which contains the image of ./max.pl. This file can then be imported into your project and used as follows:

import SWIPL from './max';

async function main() {
  const Module = await SWIPL();
  const res = Module.prolog.query('max(1, 2, 3).');
  console.log(res.next())
}

main();

Note that this procedure generates a file which imports directly from swipl-wasm/dist/loadImageDefault, so make sure that swipl-wasm is a direct dependency in your project rather than a dev dependency.

To generate the image data without it pre-loaded into SWIPL use the --image-only flag.

Running JavaScript from Prolog

This uses eval:

swipl.prolog
  .query("js_run_script(Script)", {
    Script: `console.log('hello')`,
  })
  .once();

Using with Webpack

Webpack is a JavaScript and resources bundler for large-scale frontend projects.

There is an example Webpack project in examples/webpack. It uses Asset Modules to "load" necessary .data and .wasm files. The location of these files and then fed to locateFile (see above).

The package swipl-wasm is linked into the example. In an actual project you would declare swipl-wasm as a normal dependency.

To start the example:

cd examples/webpack
npm install
npm build
npm run server

and visit http://127.0.0.1:8080. You should see the message "Hello world from Prolog".

Browser Builds

For convenience we provide deploy bundled versions of the SWI-Prolog on github pages which can be directly used in an HTML document.

There is a bundled version for each release - which can be found at the url:

https://SWI-Prolog.github.io/npm-swipl-wasm/vMajor/vMinor/vPatch/index.js

for instance v3.3.0 has the url https://SWI-Prolog.github.io/npm-swipl-wasm/3/3/0/index.js. We also have shortcuts for:

• the latest version https://SWI-Prolog.github.io/npm-swipl-wasm/latest/index.js,
• the latest of each major version https://SWI-Prolog.github.io/npm-swipl-wasm/vMajor/latest/index.js, and
• the latest of each minor version https://SWI-Prolog.github.io/npm-swipl-wasm/vMajor/vMinor/latest/index.js

Available versions can be browsed at https://github.com/SWI-Prolog/npm-swipl-wasm/tree/pages.

With this approach the following script will work

<div id="solution"></div>
<script src="https://SWI-Prolog.github.io/npm-swipl-wasm/3/3/0/index.js"></script>
<script>
  (async () => {
    const swipl = await SWIPL({ arguments: ["-q"] });
    const query = "member(X, [a, b, c]).";
    const solutionElement = document.getElementById("solution");
    const firstSolution = swipl.prolog.query(query).once().X;
    solutionElement.textContent = firstSolution;
  })();
</script>

Dynamic imports are also available with the dynamic-import.js import name and can be used as follows:

<div id="solution"></div>
<script>
  (async () => {
    const { SWIPL } = await import("https://SWI-Prolog.github.io/npm-swipl-wasm/3/3/0/dynamic-import.js");
    const swipl = await SWIPL({ arguments: ["-q"] });
    const query = "member(X, [a, b, c]).";
    const solutionElement = document.getElementById("solution");
    const firstSolution = swipl.prolog.query(query).once().X;
    solutionElement.textContent = firstSolution;
  })();
</script>

Build

The package can be built using npm. Please use npm to add new dependencies and update package-lock.json file. SWI-Prolog WebAssembly version is currently built inside Docker with Emscripten.

Development

To develop with this package, clone the repository and run:

# Install dependencies
npm ci
# Build the WebAssembly
npm run build
# Run tests
npm t

Note You need Docker and Node 16 or higher to installed build the package.

Versioning

The package uses its own versioning scheme using semver. It is detached from the versioning of SWI-Prolog itself.

To get the underlying SWI-Prolog version:

const swipl = await SWIPL({ arguments: ["-q"] });
const version = swipl.prolog
  .query("current_prolog_flag(version, Version)")
  .once().Version;

The version is returned as integer 10000 × Major + 100 × Minor + Patch.

TODO

• Integrate with SWI-Prolog CI
• TypeScript types for Prolog.js (and the Query interface)
• Use EcmaScript modules as output: https://github.com/emscripten-core/emscripten/issues/11792

License

Same as SWI-Prolog license, BSD simplified: https://github.com/SWI-Prolog/swipl-devel/blob/master/LICENSE