[antlr-interest] Re: more specific (lang independent?) actions (WAS: header sections)

[Marq Kole]

--- In antlr-interest at yahoogroups.com, Terence Parr <parrt at c...> 

<SNIP>

> > So are these handled by a generic rule like ID '{' (.)* '}'  
where the
> > stuff inside is just passed as an attribute to the template?  So
> > antlr.g doesn't have to change if some other language needs its 
own
> > special block?
> 
> Wow.  Devious thought.  I like the flexibility so any language 
target 
> could require special code sections.  We'd probably have to make it
> 
> section fields {
> ....
> }
> 
> rather than
> 
> fields {
> }
> 
> A VERY interesting idea.  C++ might need a whole slew of 
sections...

What I do like about the current approach is that is extremely easy 
to change the way separate sections are defined and used within the 
code generator. If you need different types of sections for any 
supported language, language independence becomes more of an 
theoretical issue than of practical consequences.

It is just very practical to have the

header "name" {
}

sections at the start for any global stuff, and something like

code "name" {
}

sections after the optional actions section (needed for backwards 
compatibility) in each of the lexer/parser/treewalker definitions.

The way code generation is currently handled in C++ is different 
from that in Python, but it is very easy to make customized sections 
and introduce these at the appropriate places in the code generator.

In the end, if you want to rewrite a grammar in ANTLR C++ to ANTLR 
Python, you will need to consider how each of the "language 
independent" sections translates to the concepts of the other 
language.

In the end it all comes down to correctly documenting the available 
sections for each of the supported language in the ANTLR runtime 
documentation.

Greetz,
Marq






 
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