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Tokenizer and analyzer package supporting precedence prioritized rules

, 1 Jan 2002
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A library allowing you to conveniently build a custom tokenizer and analyzer supporting precedence priorized rules

grammarIDE   Evaluation

Introduction

This library has its origin in some study project I am currently working on. All source code is covered by the LGPL - this means you can freely use the code in any project (commercial or non-commercial).

How it works

The tokenizer uses a hierarchical map structure to store the tokens, and should be as fast as the paragon lexx (at least n*O(lexx) Smile | :) . The analyzer does not have the restriction of being a LALR(1) analyzer (if used correctly), has some caching capabilities and allows resolution of literal tokens. It also supports a precedence prioritized rule set.

All projects make heavy use of the STL. Because the STL implementation shipped with MSVC6 is not the best option, you should download the STL Port 4.5.1 implementation freely available at www.stlport.org. I have now managed to get rid most of the C4786 warnings (hint: switch /FI).

How to setup the analyzer/tokenizer

A typical rule definition for a simple expression evaluator looks like this:

std::tstringstream init(
    "[seperators]\n"
    "200:+\n"       "201:-\n"
    "202:*\n"       "203:/\n"
    "204:^\n"       "205:;\n"
    "206:(\n"       "207:)\n"
    "' Whitespace tokens:\n"
    "0: \n"         "0:\t\n"
    "0:\\n\n"       "0:\\r\n"
    "[rules]\n"
    "300:numbers\n"
    "[grammar]\n"
    "401:{.expr}=100:{.expr}{$+}{.expr}\n"
    "402:{.expr}=100:{.expr}{$-}{.expr}\n"
    "403:{.expr}=99:{.expr}{$*}{.expr}\n"
    "404:{.expr}=99:{.expr}{$/}{.expr}\n"
    "405:{.expr}=98:{.expr}{$^}{.expr}\n"
    "406:{.expr}=0:{$(}{.expr}{$)}\n"
    "400:{.expr}=0:{!number}\n"
    "500:{.line}=0:{.expr}{$;}\n");

This initializes the tokenizer to recognize the separators '+', '-', '*', '/', '^', ';', '(', ')' and to skip the usual white space characters, and initializes the analyzer to recognize the math rules '+,*,-,/,^' and declares that '*' has a higher priority than '+', for example.

The interface class

Usually you have to deal only with one class, cxtPackage. This class exports all methods needed to access the library. Some of them are:

  • vSetInputStream() - sets the input stream Smile | :)
  • vSetDelimeterIDs() - can be used to set the end-of-statement tokens, in C++ this could be ';'
  • nReadUntilDelimeter() - parses the input stream until the next delimiting token is found or the end of the input stream is reached
  • papbCheckForRule() - analyzes the token stream for a given rule and returns a parse tree (if successful)
  • vRebalance() - rearranges the parse tree according to the precedence priority rules

Those are the most important ones. For more details please see the sample project or check the page http://www.subground.cc/devel which will have some minimal documentation on the classes available for download soon.

New: The grammar IDE

The new grammar IDE included in the complete download provides a environment to develop and test analyzer rulesets. It has some syntax-highlighting features, shows errors by marking the lines in the editor and has an integrated test environment to live-check the results of the ruleset. I have no documentation yet and the IDE is still early beta and it has some cosmetic bugs (for example, it is possible to insert via clipboard RTF-formatted text into the editor Smile | :) , but most of it is already usable.

The sample projects

There are two sample projects included in the complete download. One is an almost-empty sample application you can easily use to explore the library, and the other project, simpleCalc, shows how to use the library to build a simple expression evaluator in 200 lines. A step-by-step explanation on how the sample works is here.

How to use it in own projects

Make sure to insert the projects cxTokenizer, cxAnalyzer and cxtPackage in the workspace of your project. Adjust the dependencies of your project to depend on cxtPackage (which itself depends on cxAnalyzer, which in turn depends on cxTokenizer). If your project doesn't use the MFC, you have to include the file common.cpp which is located in the base directory of the project files in your project. If you have problems or questions, feel free to mail them to alexander-berthold@web.de. For the most recent updates, see also http://www.subground.cc/devel

Updates

  • 2002-01-02
    C++ (w/o templates and pre-processor) grammar is now included. See also here.
  • 2001-12-29
    Fixed small bug in analyzer. IDE download now includes a not yet complete C grammar.
  • 2001-12-27
    Updated Homepage-URL to ad-free host.
  • 2001-12-26
    Uploaded new release including the grammarIDE and some enhancements in the analyzer.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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About the Author

Alexander Berthold
Web Developer
Germany Germany
No Biography provided

Comments and Discussions

 
General'lexx' and 'yacc' and Antlr PinmemberPaul Selormey25-Dec-01 20:09 
GeneralRe: 'lexx' and 'yacc' and Antlr PinmemberAlexander Berthold25-Dec-01 23:52 
Hi, thanks for your comment.
Intentionally i did not try to get too deep into 'lexx' and 'yacc' before writing this library, so i do not really have experience using them.
 
But i think 'cxtPackage' is comparable to lexx and yacc. In fact, i am currently writing a C++ compiler built upon 'cxtPackage' and w/o templates i managed up to now to implement >70% of the language grammar using cxtPackage, even complex expressions like (int *(const *a[5])[3]) can be parsed without modifications.
I also never took a closer look at 'Antlr', but i will in the near future.
 
In terms of speed i'd say 'cxtPackage' could be even faster compared to lexx/yacc, but i have never tried this also.
 
Regards + Happy new year,
Alexander Berthold

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