js-slang

Open-source implementations of the programming language Source. Source is a series of small subsets of JavaScript, designed for teaching university-level programming courses for computer science majors, following Structure and Interpretation of Computer Programs, JavaScript Adaptation (https://sicp.comp.nus.edu.sg).

Usage

To run in native, set isNativeRunnable to true here: https://github.com/source-academy/js-slang/blob/master/src/index.ts#L29

To build,

$ git clone https://github.com/source-academy/js-slang.git
$ cd js-slang
$ yarn
$ yarn build

To try out Source in a REPL, run

$ node dist/repl/repl.js [chapter] # default: 1

If you wish, you can pass in a file path instead, to evaluate some Source before initialising the REPL It will be run in Source chapter 4.

$ node dist/repl/repl.js [path/to/file]

or alternatively, install js-slang and run

$ npm -g install js-slang   # Install js-slang
$ js-slang [chapter] # default: 1

Documentation

Source is documented here: https://sicp.comp.nus.edu.sg/source/

To build the documentation, run

$ git clone https://github.com/source-academy/js-slang.git
$ cd js-slang
$ npm install # If additional permissions are required, run sudo npm install
$ yarn jsdoc  # to make the web pages in js-slang/doc/source
$ cd doc
$ make        # to make the PDF documents using LaTeX

Documentation on the Source libraries are generated from inline documentation in the library sources. The libraries are in repository cadet-frontend, which is assumed to be located in ../cadet-frontend, from the root of this repo. The command yarn jsdoc makes the documentation available in folder doc/jsdoc/libraries/. The script jsdoc provides an installation command to deploy the documentation via scp on a server: yarn jsdoc install

Testing

js-slang comes with an extensive test suite. To run the tests after you made your modifications, run yarn test. Regression tests are run automatically when you want to push changes to this repository. The regression tests are generated using jest and stored as snapshots in src/__tests__.

After modifying js-slang, carefully inspect any failing regression tests reported in red in the command line. If you are convinced that the regression tests and not your changes are at fault, you can update the regression tests as follows:

$ yarn test -- --updateSnapshot

Error messages

To enable verbose messages, have the statement "enable verbose"; as the first line of your code.

There are two main kinds of error messages: those that occur at runtime and those that occur at parse time. The first can be found in interpreter-errors.ts, while the second can be found in rules/.

Each error subclass will have explain() and elaborate(). Displaying the error will always cause the first to be called; the second is only called when verbose mode is enabled. As such, explain() should be made to return a string containing the most basic information about what the error entails. Any additional details about the error message, including specifics and correction guides, should be left to elaborate().

Please remember to write test cases to reflect your added functionalities. The god of this repository is self-professed to be very particular about test cases.

Using your js-slang in local Source Academy

A common issue when developing modifications to js-slang is how to test it using your own local frontend. Assume that you have built your own cadet-frontend locally, here is how you can make it use your own js-slang, instead of the one that the Source Academy team has deployed to npm:

$ cd js-slang
$ yarn build
$ cp -r dist ../cadet-frontend/node_modules/js-slang

Then start frontend and the new js-slang will be used.