[antlr-interest] Multiple-target parsers, and extending without overriding

[Gavin Lambert]

At 13:06 8/01/2011, Geoffrey Romer wrote:
 >But that seems like it's not always possible. So far as I can 
tell,
 >there's no way to keep syntactic or semantic predicates outside 
the
 >grammar (now would it be very desirable if you could). Keeping 
rule
 >arguments and return values outside the grammar is a 
contradiction
 >in terms. I can't even find a way to skip whitespace without
 >writing code in the target language.  Am I missing something?

One way to do it depends on how compatible the two languages are, 
particularly with method call syntax (for example, C++ and Java 
have compatible method call syntax).  If this is the case then you 
can just write every predicate as a call to a method (left 
undefined in the grammar), and then either subclass or superclass 
the resulting parser class to provide the actual 
implementation.  (You can do something similar with C, but you'd 
have to call global functions, and possibly alter the parameters a 
little.)