LRSTAR: LR(*) parser generator for C++


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LRSTAR + DFA is Open-Source Software with BSD license.

  • More complete than Yacc/Bison parsers.
  • Faster than ANTLR 4 parsers using C++ target.
  • LRSTAR: LR(*) parser generator v 11.0

  • Creates LR(*) parsers
  • Reads grammar notation with EBNF operators (+,*,?)
  • Grammars are independent from code
  • Handles context-sensitivity (e.g. typedef in C)
  • Parsers have a symbol-table builder
  • Parsers do AST construction and traversal calling your code-generation functions.
  • Includes Visual Studio IDE Community projects
  • DFA: fast lexer generator v 11.0

  • Creates DFA compressed-matrix lexers
  • Lexers do keyword recognition
  • New In Version 11.0

    (1) The LR(*) nondeterministic parsing has been greatly improved.
    (2) Reads Yacc/Bison & ANTLR grammars (with some limitations).
    (3) Skeleton files are not used anymore which makes development simpler.
    (4) Parser actions (funtion arguments) have been improved.
    (5) More than one parser (language) can exist in an application.

    LR(*) Parsers

    LRSTAR creates an LR(*) parser, if necessary. If your grammar is LALR(1), then it creates an LALR(1) parser. If you grammar is LR(1), then it creates an LR(1) parser. If your grammar is neither, because of conflicts, it will create an LR(*) parser, if you set k to 2, 3 or more. LRSTAR will tell you whether your grammar is LALR(1), LR(1) or neither. An LR(*) parser does lookahead at parse time to resolve conlicts. Therefore, if the language you are trying to parse is LR(k), where k > 1, you should be able to parse it. In our test file it needed to lookahead 13 tokens in one situation. The LR(*) parsing algorithm is efficient and does not impact the parsing speed very much.

    DFA Lexical Analyzers

    A DFA lexer is a finite-state automata.  DFA is the fastest recognition algorithm (5 times the speed of PDA's).  DFA's work fine for most programming languages.  You may include the keywords of your language in the lexical grammar which makes keyword recognition as fast as possible. The data structure created by DFA is a compressed-matrix. See the comparison page to find out how DFA compares to flex and re2c.

    Parser Speed

    Parsing speed is comparable to Yacc/Bison generated parsers. However, LRSTAR can generate slightly faster parsers, if you use the optimize option (/o). Probably, the speed advantage goes to LRSTAR, because it generates parsers which automatically build a symbol table and an abstract-syntax tree (AST). Compared to ANTLR? I did a test of ANTLR 4.8 using the C++ target and discovered that the ANTLR parser was taking 15 seconds, whereas the LRSTAR parser was taking 0.1 seconds, to process a C source code file of 227,000 lines.

    Context Sensitivity

    The "typedef" declaration in the C and C++ languages is a context sensitive issue.  This cannot be solved by upgrading from LALR(1) to LR(1) or LR(k).  It requires making use of a symbol table while parsing and this allows even an LALR(1) parser to handle this context sensitive issue.  LRSTAR has this feature built into the grammar notation, making life easy for a user.

    (c) Copyright Paul B Mann 2020.  All rights reserved.