[antlr-interest] pretty printing in the c target

[Robert Soule]

Hi,

I am trying to write a pretty printer for my input language. In java,
I read in the source, convert to the AST, then use a tree grammar
to call the StringTemplates, and everything works fine. However,
I need to use C as the target language, and there isn't a StringTemplate
implementation in C.

I looked at the examples that are available on the antlr.org website,
but the only ones that pretty print are toy examples, and simple append
the character strings to the text contained in the token literals. This
isn't really a feasible approach in my language. So, what I've ended up
doing is following a pattern more or less like the following:

someRule
returns [pANTLR3_STRING result]
@init {result = factory->newRaw(factory);}
: ^(SOMETOKEN anotherRule thirdRule)
{
  $result->append($result, "Start\n");
  $result->appendS($result, $anotherRule.result);
  factory->destroy(factory, $aotherRule.result);
  $result->appendS($result, $thirdRule.result);
  factory->destroy(factory, $thirdRule.result);
  $result->append($result, "\n\n");
}

However, I've encountered a few problems with this approach. First,
when I call factory->close(..) at the end of my program, I get a double
free problem, and I don't see in the API where I can call remove on
the string from the factory. However, more troubling is that when the
return of one of the rules like anotherRule is composed of only
small literal strings (like "()"),  then calling destroy on the result sometimes
frees too much memory, so that I cause problems for "thirdRule".
Moreover, this just seems like an awkward way to build up my output
string.

Since this seems like a pretty common task, I was wondering if
there is a common, recommended way of doing this?

thank you,
Robert
thank you,
Robert