error-checking algorithm for the redefinition

[Kohsuke KAWAGUCHI <kohsuke.kawaguchi@eng.sun.com>]

Here is a summarized version of the algorithm that (I hope) correctly
handle inclusions, definitions, and redefinitions.


fields of RefPattern (of JTREX)
-------------------------------

combineMethod: (none/interleave/choice)
    specifies what method is used to combine patterns.

haveHead: boolean
    true if this named pattern already has a "head".
    a "head" is a <define> declaration without @combine.

redefinition:
    (a) notBeingRedefined
    (b) beingRedefinedAndNoOriginal
    (c) beingRedefinedAndOriginal


algorithm
---------

When an <include> element is encountered,

processInclude() {
    variable tmp;
    
    for( each <define> under <include> ) {
        processDefine();
        store values of the above three fields to tmp;
    }
    
    // to correctly handle grammars like [*1],
    // we need two separate loops.
    
    for( each <define> under <include> ) {
        reset values to (none,false,(b)).
    }
    
    process included pattern.
    
    for( each redefined pattern in this <include>) {
        if( the redefinition field is (b) )
            redefinedButNoOriginalFoundError();
        
        restore the values of the three fields from tmp;
    }
}

// normal processing of <define>
processDefine() {
    // parse the body of <define>
    p = parseBody();
    
    if( the redefinition field is (a) ) {
        adopt p as the pattern for this name.
        don't forget to honor @combine.
    } else {
        set the redefinition field to (c).
        discard p.
    }
    
    update the combineMethod field and the
    haveHead field according to @combine.
}



[*1]
If defining a pattern more than once in the same file is allowed,
then a measure has to be taken to process the following pattern.

<include href="...">
  <define name="foo"/>
  <define name="foo"/>
</include>


--
Kohsuke KAWAGUCHI                          +1 650 786 0721
Sun Microsystems                   kohsuke.kawaguchi@sun.com