Re: Compiler compiler that supports dynamic keywords?

> I'm interested in building a parser that dynamically determines the
> lexical structure of particular rule element at runtime. For example,
> consider the following rule (in JavaCC pseudocode):
>
> "Hello" (
> <nameType1> RuleForRestOfSentenceType1()
> |
> <nameType2> RuleForRestOfSentenceType2()
> )
>
> The key is that the definition of <nameType1> and <nameType2> needs
> tobe changeable at runtime. . . .


Yes, this is a known solved problem. As you guess, essentially it is
a variation on the keywords problem. The solution is to intervene
between the lexer and the parser with a phase called a "screener".
[Frank De Remer coined the term. (Please excuse me if I have
mispelled the last name slightly. I recall it as one word, but a
reference I have cites him as shown.)]


The screener looks up words in a (set of) dictionary(ies) and finds
"token types" for those words to replace the default token type.
There are more details on the technique in the June 99 SIGPLAN
Notices.


There are also parser generators that encourage this model of
organizing ones lexing and parsing by building it into their framework
(Anagram(outputs C) and Yacc++(outputs C++)). However, I am not aware
of any that support the model and produce Java as output. I'm
currently aware of 4 Java parser generators, ANTLR, CUP, JavaCC, and
VisualParse++.


Hope this helps,
-Chris


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