apg-js-examples/src/look-ahead/anbncn.js

Examples of using the suite of apg-js applications and libraries.

// copyright: Copyright (c) 2024 Lowell D. Thomas, all rights reserved<br>
//   license: BSD-2-Clause (https://opensource.org/licenses/BSD-2-Clause)<br>
//
// Generated by apg-js, Version 4.4.0 [apg-js](https://github.com/ldthomas/apg-js)
module.exports = function grammar(){
  // ```
  // SUMMARY
  //      rules = 5
  //       udts = 0
  //    opcodes = 20
  //        ---   ABNF original opcodes
  //        ALT = 0
  //        CAT = 4
  //        REP = 3
  //        RNM = 6
  //        TLS = 6
  //        TBS = 0
  //        TRG = 0
  //        ---   SABNF superset opcodes
  //        UDT = 0
  //        AND = 1
  //        NOT = 0
  //        BKA = 0
  //        BKN = 0
  //        BKR = 0
  //        ABG = 0
  //        AEN = 0
  // characters = [97 - 99]
  // ```
  /* OBJECT IDENTIFIER (for internal parser use) */
  this.grammarObject = 'grammarObject';

  /* RULES */
  this.rules = [];
  this.rules[0] = { name: 'AnBnCn', lower: 'anbncn', index: 0, isBkr: false };
  this.rules[1] = { name: 'Prefix', lower: 'prefix', index: 1, isBkr: false };
  this.rules[2] = { name: 'ConsumeAs', lower: 'consumeas', index: 2, isBkr: false };
  this.rules[3] = { name: 'AnBn', lower: 'anbn', index: 3, isBkr: false };
  this.rules[4] = { name: 'BnCn', lower: 'bncn', index: 4, isBkr: false };

  /* UDTS */
  this.udts = [];

  /* OPCODES */
  /* AnBnCn */
  this.rules[0].opcodes = [];
  this.rules[0].opcodes[0] = { type: 2, children: [1,3,4] };// CAT
  this.rules[0].opcodes[1] = { type: 12 };// AND
  this.rules[0].opcodes[2] = { type: 4, index: 1 };// RNM(Prefix)
  this.rules[0].opcodes[3] = { type: 4, index: 2 };// RNM(ConsumeAs)
  this.rules[0].opcodes[4] = { type: 4, index: 4 };// RNM(BnCn)

  /* Prefix */
  this.rules[1].opcodes = [];
  this.rules[1].opcodes[0] = { type: 2, children: [1,2] };// CAT
  this.rules[1].opcodes[1] = { type: 4, index: 3 };// RNM(AnBn)
  this.rules[1].opcodes[2] = { type: 7, string: [99] };// TLS

  /* ConsumeAs */
  this.rules[2].opcodes = [];
  this.rules[2].opcodes[0] = { type: 3, min: 0, max: Infinity };// REP
  this.rules[2].opcodes[1] = { type: 7, string: [97] };// TLS

  /* AnBn */
  this.rules[3].opcodes = [];
  this.rules[3].opcodes[0] = { type: 2, children: [1,2,4] };// CAT
  this.rules[3].opcodes[1] = { type: 7, string: [97] };// TLS
  this.rules[3].opcodes[2] = { type: 3, min: 0, max: 1 };// REP
  this.rules[3].opcodes[3] = { type: 4, index: 3 };// RNM(AnBn)
  this.rules[3].opcodes[4] = { type: 7, string: [98] };// TLS

  /* BnCn */
  this.rules[4].opcodes = [];
  this.rules[4].opcodes[0] = { type: 2, children: [1,2,4] };// CAT
  this.rules[4].opcodes[1] = { type: 7, string: [98] };// TLS
  this.rules[4].opcodes[2] = { type: 3, min: 0, max: 1 };// REP
  this.rules[4].opcodes[3] = { type: 4, index: 4 };// RNM(BnCn)
  this.rules[4].opcodes[4] = { type: 7, string: [99] };// TLS

  // The `toString()` function will display the original grammar file(s) that produced these opcodes.
  this.toString = function toString(){
    let str = "";
    str += ";\n";
    str += "; text book example of a phrase which\n";
    str += "; cannot be described with a context-free grammar\n";
    str += "; but can be described using syntactic predicates\n";
    str += ";\n";
    str += "AnBnCn    = &Prefix ConsumeAs BnCn\n";
    str += "Prefix    = AnBn \"c\"\n";
    str += "ConsumeAs = *\"a\"\n";
    str += "AnBn      = \"a\" [AnBn] \"b\"\n";
    str += "BnCn      = \"b\" [BnCn] \"c\"\n";
    return str;
  }
}