plt.js

A programming language design prototyping tool

Overview

plt.js is an environment for writing and testing programming language grammars. You write your language's grammar and example code in an HTMLish syntax, and plt.js will parse your code against your grammar and display the result. It will also provide you with a REPL interface into your language, so you can get a feel for it right away.

It looks like this:

<grammar>
  start       = '(' '+' space a:number ' ' b:number space ')' { return a + b }
  number      = d:digit+ { return parseInt( d.join('') ) }
  digit       = [0123456789]
  space       = ' '*
</grammar>

<h3>Addition</h3>
<code>(+ 5 10)</code>
<code>(+7 13)</code>
<code>(+ 7 13)</code>

Which would output

Addition

(+ 5 10)
↳ 15
(+7 13)
↳ 20
(+ 7 13)
↳ 20

And if you type (+ 12 89) and hit enter, you should see

> (+ 12 89)
101

Try it. It's great fun.

Usage

1. Download and extract plt.js
2. Copy example.html to your-language.html
3. Open your-language.html in a browser
4. Replace the <title> tag with the name of your language
5. Replace the <grammar> tag with the PEG grammar of your language
6. Write examples of correct syntax in <code> tags. plt.js will parse them and display the result
7. Write examples of incorrect syntax in <code bad> tags. plt.js will parse them and display the result
8. Write any other HTML to annotate your examples
9. Open your-language.html file in a browser

plt.js is designed to work offline. The only constraint is that your your-language.html file must be in the same folder as the js/ folder where plt.js keeps its files.

Testing

To test your language, add the expect tag to your code examples:

<code expect="15">(+ 5 10)</code>
<code expect="20">(+7 13)</code>
<code expect="20">(+ 7 13)</code>

Errors will appear inline:

Name

PLT is short for Programming Language Theory, the branch of computer science that deals with the design and implementation of programming languages.

Acknowledgments

plt.js comes out of my time as an Eyebeam Fellow exploring code as a medium of self expression. It was further developed as a teaching tool for my programming language design class at NYU ITP.

Legal

Copyright © 2014 Ramsey Nasser. Released under the MIT License.

PEG.js Copyright © 2010–2013 David Majda

Sugar.js Copyright © 2011 Andrew Plummer