[antlr-interest] Translating from one language to another

[Loring Craymer]

If the structure of the AST you print from is determined by luck, then you have serious design problems.  For complex translation problems, the "art of ANTLR" is in transforming ASTs (possibly across several passes) to capture the semantics of the input language into tree syntax and thence to output semantics.  If you have any desire to build auxilliary tools for the language you are translating from, then you really want to take the effort to build a usable AST:  you will find that that makes a big difference in both maintainability and flexibility for other applications.

--Loring



----- Original Message ----
> From: Mark Wright <markwright at internode.on.net>
> To: David Tauzell <dave at tauzell.org>
> Cc: antlr-interest at antlr.org
> Sent: Tuesday, July 22, 2008 9:55:23 AM
> Subject: Re: [antlr-interest] Translating from one language to another
> 
> Of course the ANTLR book is essential.
> 
> The syntax directed translation approach (generate code from the
> AST) would be easy if you are lucky that your generated code is
> in a very similar structure to the source language.
> 
> This article by Andy is brilliant:
> 
> http://jazillian.com/articles/treewalkers.html
> 
> In my situation, which is different to yours, I thought
> my AST was not in the right form to generate the code using
> string template, Andy's article just reinforced this for me, which
> really helped.
> 
> I think string template is great.  What I did was I generated
> a completely new tree with all the information I need in the
> right places to generate the code, then used string template to
> generate it.  So basically, I used Andy's approach (I manually
> walked the AST looking for stuff for the new tree which I entered
> into some data structures), manually walked parts of the symbol table
> (while looking up more stuff in the  symbol table and other data
> structures), generated a new tree, and used string template.
> 
> If AST is not in the right format to generate the code, then
> one approach is to figure out some way to transform and
> augment it, possibly with new subtrees, or generate a new tree.
> 
> On Tue, 22 Jul 2008 11:38:15 -0400
> Andy Tripp wrote:
> 
> > A "quick and dirty" alternative approach to StringTemplate is
> > to write some code that just walks your AST, printing out code.
> > This: http://www.jazillian.com/antlr/emitter.html
> > just walks a Java AST and prints Java code.
> > 
> > David Tauzell wrote:
> > > I'd like to translate from language A to java.  I've written a
> > > grammar that parses language A and generates an AST.   The language
> > > is mostly like java, except there are a few cases where I'll need
> > > to change the input.  For example, something like:
> > > 
> > >     a.b.c.d = foo
> > > 
> > > will be converted to
> > > 
> > >     a.get("b").get("c").get("d").setValue(foo)
> > > 
> > > Other stuff like:
> > > 
> > >    if( foo == "bar") {
> > >       ...
> > >    }
> > > 
> > > can stay like it is.
> > > 
> > > I'm not sure what is the best way to proceed.  Should I somehow use 
> > > StringTemplate?  Should I walk the AST and generate output? Is this 
> > > question to vague? Do I just need to buy the ANTLR book and learn
> > > more about ANTLR?
> > > 
> > > Thanks,
> > >     Dave
> > > 
> > > 
> > 
> 
> 
> --