https://github.com/codebox/top-down-parser

A simple top-down parser written in JavaScript
https://github.com/codebox/top-down-parser

es6 javascript parser

Last synced: 7 months ago
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A simple top-down parser written in JavaScript

• Host: GitHub
• URL: https://github.com/codebox/top-down-parser
• Owner: codebox
• License: mit
• Created: 2018-12-08T13:40:58.000Z (about 7 years ago)
• Default Branch: master
• Last Pushed: 2018-12-27T13:21:31.000Z (about 7 years ago)
• Last Synced: 2025-05-25T04:21:34.323Z (8 months ago)
• Topics: es6, javascript, parser
• Language: JavaScript
• Homepage: https://codebox.net/pages/top-down-parser-in-javascript
• Size: 61.5 KB
• Stars: 4
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

          
# Top-Down Parser

A simple top-down parser written in JavaScript. Every so often I need to write a parser, and keep forgetting how the recursion works.

 This is a simple- and general-as-possible implementation that I can refer back to in the future.

 

To use the parser, call the `buildParser()` function with a single string argument containing the grammar. 

Each production rule in the grammar should be on a separate line, and the symbol should be followed by the character sequence `->`,

 and then by the substitutions. The symbol `|` is used as a delimiter on the RHS of a rule if there are multiple valid substitutions. 

 

By default the start symbol is the text `START` and `ε` is used to represent an empty string, 

 alternate values can be supplied when calling `buildParser()`.  

I have used several ES6 language features in the code, so this won't work in older browsers.

## Example

    const parser = buildParser(`

        START -> EXPR

        EXPR  -> NUM | NUM OP EXPR

        NUM   -> 0 | 1 | 2 | 3 | 4

        OP    -> + | - | * | /

    `);

    

    parser.parse('1 + 2')

Will return:

    {

        'remainder : '',

        'tree' : {

            'START' : [

                {'EXPR' : [

                    {'NUM' : ['1']},

                    {'OP' : ['+']},

                    {'EXPR' : [

                        {'NUM' : ['2']},

                    ]}

                ]}

            ]

        }

    }