[antlr-interest] Re: ANTLR 3.0 question about common actions

[Thomas Brandon]

While considering actions you might think about the syntax of 
actions, especially if you are planning to break backwards 
compatibility in this area. This is a bit of a nasty area in the 
Antlr parser\lexer. As action blocks can include arbitrary text 
(from the point of view of the Antlr parser which is ideally target-
language specific), some tricky handling of them is required. 
Currently the Antlr lexer looks for the matching end marker (']' for 
arg actions, '}' for normal actions) with special handling for 
nested target-language blocks using []\{} and appearances in 
comments and strings.
This means the current Antlr grammar is somewhat target language 
specific, limited to languages with C++ style comments (// single 
line, /* */ multi-line) and chars\strings ('' and "", pretty 
universal). Consider for instance a VB code generator with ';' as 
comment delimeter (not likely to be a problem).
And care must be taken with delimeters inside actions, for instance, 
using '<' and '>' for templated actions as Ter suggest would seem 
problematic. What do you do about "{if (some-condition) <somefunc
(i>x)>;}".
Having more complex action delimeters would seem to be a good 
idea, "<a:skip()>" ('a' for action) while more verbose is less 
likely to clash with a desired target language expression.

Tom.
--- In antlr-interest at yahoogroups.com, Terence Parr <parrt at c...> 
wrote:
> 
> On Jul 28, 2004, at 1:48 PM, Monty Zukowski wrote:
> > Currently you have an escape mechanism that says "this is all 
target
> > language
<snip>
> NEWLINE : '\n' {if (some-condition) <skip()>;} ;
<snip> 
> Ter
> --
> CS Professor & Grad Director, University of San Francisco
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