[antlr-interest] Newbie Q: Duplicating nodes from parse into AST

[Austin Hastings]

FWIW,

I see on the archive that "Christian Andersson" had essentially the same 
problem as me, wrt splitting a declaration like:

int a,b;

into an AST like ^(int a) ^(int b).

FWIW, Christian and others, I worked around the problem by doing the 
trick detailed under "Creating Nodes with Arbitrary Actions" in the 
Definitive ANTLR Reference. Here's what my solution looks like, abbreviated:

declaration
    : type=decl_type_spec!
      declarator[$type.tree]
      (',' declarator[$type.tree])*
    ;

decl_type_spec : 'int' ; /* or whatever */

declarator[CommonTree type]
    : decl_prefix_expr   -> ^(DECL {$type} decl_prefix_expr)
    ;

decl_prefix_expr : /* Matches identifiers, pointers, blah blah blah. */

The key to this trick is the parameterized rule "declarator," which 
accepts the type information as an argument. The "declaration" rule 
matches the type name, qualifiers, storage class, yadda yadda yadda, 
groups it into a "type" subtree, and passes that subtree to "declarator" 
every time it matches one. The declarator node emits the AST including 
type data.
 
Yes, as I posted the other day, I think it should be possible to do this 
with a rewrite rule. Certainly there is an example in Parr's book that 
indicates this should be possible. But this works today.

Enjoy,

=Austin