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simple java framework for ragel based parsers
Java
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README.markdown
buildfile

README.markdown

how to use this project

The buildr buildfile contains to rake tasks for generating ragel parsers and cleaning up the generated ragel parsers: buildr ragel : generate ragel parsers buildr ragel_clean : remove generated ragel parsers

Remember to call buildr ragel_clean before you do a commit.

introduction

The parsr projekt is a framework for event based parsing using the ragel parser generation framework. You can write your parser definition in ragel and use the framework for generating and processing parsing events.

Parsing events are thrown as user actions in the ragel machine definition, (see chapter 3 of the ragel user guide) and are processed by the ContentHandler which is implemented by you.

how to create a parser

To create a Parser you have to create a file with the following contents and the ending .rl for ragel. The filename should match the class name and the folder should match the package. In the example the filename would be SomeParser and the package com.foo.bar.

%% machine someparser;
package com.foo.bar;

import de.entwicklerland.parsr.Parser;

public class SomeParser extends Parser {

%% write data;
%% write init;
  
  public void parse(char[] data) {

    int pe = data.length;

    %% write exec;

    %%{
      # machine definition
      action anyChar {
          write();
      }
      
      # machine instantiation
      main := any $anyChar;
    }%%
  }

}

After that call buildr ragel to generate the parser class from the parsr definition. You may now modify the maschine definition.

content processing methods

To process the input stream you may use the following methods of the parser:

  • Parser.write() to write the current processed character to the outputstream, which is a sort of echo back the input stream to the output stream.

  • Parser.beginMatch("eventname") to start matching a region

  • Parser.endMatch("eventname") to end matching a region, calling endMatch generates an event for the content handler.

  • Parser.shrink(int) method to shrink the buffer of the buffered input stream

how to use the parser

the data sink is filled by the content handler

  • create a data sink (OutputStream)
  • instantiate the parser
  • create a content handler by implementing the ContentHandler interface
  • register the content handler on the parser to the events it should process
  • call one of the parse methods on the parser to process the input
// create data sink
ByteArrayOutputStream output = new ByteArrayOutputStream();
  
// instantiate parser 
Parser parser = new SomeParser();

// create content handler implementation  
ContentHandler handler = new ContentHandler() {
    @Override
    public void process(Match match, StringBuilder buffer, OutputStream output) throws IOException {
      String content = match.getContent(buffer);
        String event = match.getEvent();
                
        // write event and content to output, separated by a colon
        output.write(content.getBytes());
        output.write(':');
        output.write(event.getBytes());
            
    }
};
        
// register content handler to all parsing events
parser.registerToAll(handler);
        
// process input 
parser.parse(input, output);

test the parser

You may use the ParserValidator.java class to validate the parsing behaviour. Have a look at the existing tests on how to use the ParserValidator.java.

debugging

An endLastMatch() that is executed before a beginMatch() will result in an an IllegalStateException. You may want to use the logMark() method to debug such a case.

java.lang.IllegalStateException: empty marker stack: trying to close marker at position [75]
   input consumed[aaaaa
some\
bbbbbbccccc] at de.entwicklerland.parsr.Parser.endLastMatch(Parser.java:100) at de.entwicklerland.parsr.codeblock.CodeBlockParser.parse(CodeBlockParser.java:327) at de.entwicklerland.parsr.Parser.parse(Parser.java:70)

Since the user actions are executed in sequence, you have to put logMark() before the endLastMatch() action in the user actions.

enable syntax highlighting for ragel in vim

  1. copy ragel.vim to ~/.vim/syntax
  2. create/modify file ~/.vim/filetype.vim and add:
augroup filetypedetect
au BufNewFile,BufRead *.rl setf ragel
augroup END

ragel specifics

priorities

  • unnamed priorities are valid for the whole instantiation of a maschine !

guarded concatenation

  • to escape from an any matching sequence one can use (entry-)guarded concatenation of maschines
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