Parse::RecDescent - Excluding a Subset of Atoms From a Production Rule

Incognito has asked for the wisdom of the Perl Monks concerning the following question:

My terminology may be incorrect, but I have a grammar that needs to accept a set of atoms, minus a small subset of atoms...

Sample Grammar

ReservedWord:    
                       Keyword |
                       FutureReservedWord
    
Keyword:               
                       'break'    | 'else'       | 'new'  

FutureReservedWord: 
                       'abstract' | 'enum'       | 'int'      
                       'short'    | 'interface'  | 'static' 

Identifier:            IdentifierName

IdentifierName:        /[\$_a-zA-Z][\$_a-zA-Z0-9]*/
[download]

The Problem

I actually want the Identifier: production to be something like:

IdentifierName but not ReservedWord
[download]

meaning that we want all possible words EXCEPT those found in ReservedWord (which can get quite large). I do not believe that this can be done using negative lookahead or <reject>...

Oh mighty gods (and <grinning> semi-gods), is this even possible? If not, hours of work are lost and I shall sob quietly in my dark and damp corner. Any ideas?

Comment on Parse::RecDescent - Excluding a Subset of Atoms From a Production Rule Select or Download Code

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•Re: Parse::RecDescent - Excluding a Subset of Atoms From a Production Rule by merlyn (Sage) on Mar 14, 2002 at 23:38 UTC
Same solution as the thing I posted earlier today. Negative lookahead. `Identifier: ...!ReservedWord IdentifierName` [download] -- Randal L. Schwartz, Perl hacker	[reply] [d/l]
Re: Parse::RecDescent - Excluding a Subset of Atoms From a Production Rule by maverick (Curate) on Mar 14, 2002 at 23:39 UTC
How about using something like: `Identifier: ReservedWord { print "can't use reserved word $item[1]\n"; # Do the thing that makes P::RD throw an error } \| IdentifierName` [download] There is a way in P::RD to create 'error productions' I just don't remember what you have to do to make the matching of a production be a syntax error in the input. /\/\averick perl -l -e "eval pack('h*','072796e6470272f2c5f2c5166756279636b672');"	[reply] [d/l]