ANTLR Template translator match part of grammar - antlr

Question

I wrote a grammar for a language and now I want to treat some syntactic sugar constructions, for that I was thinking of writing a template translator.
The problem is I want my template grammar to translate only some constructions of the language and leave the rest as it is.
For example:
I have this as input:
class Main {
int a[10];
}
and I want to translate that into something like:
class Main {
Array a = new Array(10);
}
Ideally I would like to do some think like this in ANTLR
grammer Translator
options { output=template;}
decl
: TYPE ID '[' INT ']' -> template(name = {$ID.text}, size ={$INT.text})
"Array <name> = new Array(<size>);
I would like it to leave the rest of the input that doesn't match rule decl as it is.
How can I achieve this in ANTLR without writing the full grammar for the language ?

Answer 1

I would simply handle such things in the parser grammar.
Assuming you're constructing an AST in your parser grammar, I guess you'll have a rule to parse input like Array a = new Array(10); similar to:
decl
: TYPE ID '=' expr ';' -> ^(DECL TYPE ID expr)
;
where expr eventually matches a term like this:
term
: NUMBER
| 'new' ID '(' (expr (',' expr)*)? ')' -> ^('new' ID expr*)
| ...
;
To account for your short-hand declaration int a[10];, all you have to do is expand decl like this:
decl
: TYPE ID '=' expr ';' -> ^(DECL TYPE ID expr)
| TYPE ID '[' expr ']' ';' -> ^(DECL 'Array' ID ^(NEW ARRAY expr))
;
which will rewrite the input int a[10]; into the following AST:
which is exactly the same as the AST created for input Array a = new Array(10);.
EDIT
Here's a small working demo:
grammar T;
options {
output=AST;
}
tokens {
ROOT;
DECL;
NEW='new';
INT='int';
ARRAY='Array';
}
parse
: decl+ EOF -> ^(ROOT decl+)
;
decl
: type ID '=' expr ';' -> ^(DECL type ID expr)
| type ID '[' expr ']' ';' -> ^(DECL ARRAY ID ^(NEW ARRAY expr))
;
expr
: Number
| NEW type '(' (expr (',' expr)*)? ')' -> ^(NEW ID expr*)
;
type
: INT
| ARRAY
| ID
;
ID : ('a'..'z' | 'A'..'Z')+;
Number : '0'..'9'+;
Space : (' ' | '\t' | '\r' | '\n') {skip();};
which can be tested with the class:
import org.antlr.runtime.*;
import org.antlr.runtime.tree.*;
import org.antlr.stringtemplate.*;
public class Main {
public static void main(String[] args) throws Exception {
String src = "Array a = new Array(10); int a[10];";
TLexer lexer = new TLexer(new ANTLRStringStream(src));
TParser parser = new TParser(new CommonTokenStream(lexer));
CommonTree tree = (CommonTree)parser.parse().getTree();
DOTTreeGenerator gen = new DOTTreeGenerator();
StringTemplate st = gen.toDOT(tree);
System.out.println(st);
}
}