• createVariable this algorithms is interesting
• addTokenStack using javascript label syntax + esprima lib to alter ast node.

• ENBF wiki - https://en.wikipedia.org/wiki/Extended_Backus%E2%80%93Naur_form

  • for difference between ENBF and NBF, view Advantages over BNF section

    • most outstanding ones are
      • ENBF supports optional and repetitions

  • section Table of symbols defines ENBF grammar

EBNF is widely used as the de facto standard to define programming languages

• https://condor.depaul.edu/ichu/csc447/notes/wk3/BNF.pdf

An LR parser (Left-to-right, Rightmost derivation in reverse)

https://en.wikipedia.org/wiki/LR_parser

• ability scope: LR parsers can handle a larger range of languages and grammars than precedence parsers or top-down LL parsing. Look ahead: Typically k is 1 and is not mentioned.

LR parsers differ from other shift-reduce parsers in how they decide when to reduce, and how to pick between rules with similar endings.

• deterministic: using lookahead to see the next scanned symbol, before deciding what to do with previously scanned symbols.

• Rightmost: Reductions reorganize the most recently parsed things, immediately to the left of the lookahead symbol. So the list of already-parsed things acts like a stack. This parse stack grows rightwards. The base or bottom of the stack is on the left and holds the leftmost, oldest parse fragment. Every reduction step acts only on the rightmost, newest parse fragments. (This accumulative parse stack is very unlike the predictive, leftward-growing parse stack used by top-down parsers.)

• limitation: The grammar for an LR parser must be unambiguous itself, or must be augmented by tie-breaking precedence rules.

• parsing table
• stack
• parser automata
• input stream

== parsing table

Depending on how the states and parsing table are generated, the resulting parser is called either a SLR (simple LR) parser, LALR (look-ahead LR) parser, or canonical LR parser. LALR parsers handle more grammars than SLR parsers. Canonical LR parsers handle even more grammars, but use many more states and much larger tables. The example grammar is SLR.

this includes

• calc closure for kernel items
• construct parser table
  • action part, includes (reduce/shift)
  • goto part
  • resolve rule conflicts, at resolveConflict
• semantic actions: at performAction
• build DFA of item set for a grammar. lrGeneratorMixin.canonicalCollectionInsert
• LR parser automata, at parser.parse
• an error recovery mechanism
  • 

the implementation located at lrGeneratorMixin

• https://www.geeksforgeeks.org/construction-of-ll1-parsing-table/

parser table is contruct at var ll, while the parse method(automata) is not implemented by the author. but it should be pretty straight forward.

I think decend top down implementation of LL parser is mostly straight forward and practical. Using parsing table for LL parser like this lib at var ll= location is prefered way to detect conflicts in language's gramma defination.

LR vs SLR, the key difference lies at how to process lookaheads. at SLRGenerator

    lookAheads: function SLR_lookAhead (state, item) {
        return this.nonterminals[item.production.symbol].follows;
    }

thye difference is how to construct the canonical collection. at var lr1 =

-> generator

• for parsing ENBF/NBF grammar and generate productions, action

lib
├── cli.js						// cli stuff
├── jison.js					// core code
└── util
    ├── set.js					// a set implementation
    └── typal.js				// a minin helper



tests
├── all-tests.js
├── parser
│   ├── actions.js
│   ├── api.js
│   ├── errorlab.js
│   ├── generator.js
│   ├── lalr.js
│   ├── lr0.js
│   ├── lr1.js
│   ├── parser-tests.js
│   ├── precedence.js
│   ├── slr.js
│   └── tables.js
├── performance.js
└── setup.js

• issues
• discuss

Jison generates bottom-up parsers in JavaScript. Its API is similar to Bison's, hence the name. It supports many of Bison's major features, plus some of its own. If you are new to parser generators such as Bison, and Context-free Grammars in general, a good introduction is found in the Bison manual. If you already know Bison, Jison should be easy to pickup.

Briefly, Jison takes a JSON encoded grammar or Bison style grammar and outputs a JavaScript file capable of parsing the language described by that grammar. You can then use the generated script to parse inputs and accept, reject, or perform actions based on the input.

Jison can be installed for Node using npm

Using npm:

npm install jison -g

Clone the github repository for examples:

git clone git://github.com/zaach/jison.git
cd jison/examples

Now you're ready to generate some parsers:

jison calculator.jison

This will generate calculator.js in your current working directory. This file can be used to parse an input file, like so:

echo "2^32 / 1024" > testcalc
node calculator.js testcalc

This will print out 4194304.

Full cli option list:

Usage: jison [file] [lexfile] [options]

file        file containing a grammar
lexfile     file containing a lexical grammar

Options:
   -j, --json                    force jison to expect a grammar in JSON format
   -o FILE, --outfile FILE       Filename and base module name of the generated parser
   -t, --debug                   Debug mode
   -m TYPE, --module-type TYPE   The type of module to generate (commonjs, amd, js)
   -p TYPE, --parser-type TYPE   The type of algorithm to use for the parser (lr0, slr, lalr, lr)
   -V, --version                 print version and exit

You can generate parsers programatically from JavaScript as well. Assuming Jison is in your commonjs environment's load path:

// mygenerator.js
var Parser = require("jison").Parser;

// a grammar in JSON
var grammar = {
    "lex": {
        "rules": [
           ["\\s+", "/* skip whitespace */"],
           ["[a-f0-9]+", "return 'HEX';"]
        ]
    },

    "bnf": {
        "hex_strings" :[ "hex_strings HEX",
                         "HEX" ]
    }
};

// `grammar` can also be a string that uses jison's grammar format
var parser = new Parser(grammar);

// generate source, ready to be written to disk
var parserSource = parser.generate();

// you can also use the parser directly from memory

// returns true
parser.parse("adfe34bc e82a");

// throws lexical error
parser.parse("adfe34bc zxg");

For more information on creating grammars and using the generated parsers, read the documentation.

See CONTRIBUTING.md for contribution guidelines, how to run the tests, etc.

View them on the wiki, or add your own.

Githubbers

Special thanks to Jarred Ligatti, Manuel E. Bermúdez

Copyright (c) 2009-2014 Zachary Carter

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.