RE: Compiler Design + feedback

In reply to Philip Herron, Chris F Clark said:


> Running passes over an intermediate (often tree-like) representation
> of a source text, is such a powerful idea that it is formalized in
> attribute grammars and the visitor pattern and tree rewriting
> systems and probably a dozen other ways.


Meta-S grammars effect multiple passes via predicates:


grammar X {
      S::= a<b>;
      a::= c na;
      b::= an c;
      c::= '[a-z]+';
      na::= '[0-9]+[a-z]+';
      an::= '[a-z]+[0-9]+';
};




In the above, <b> is the predicate. Whatever is accepted by a is then
repassed by b. Two parse trees result:


      abc
            123def


and


      abc123
                  def


Using predicates, what gets passed over more than once is under strict
control, and thus it is possible in many cases to localize repassing and
keep the overall performance near linear in practice.


--
Quinn Tyler Jackson

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