Antlr AST tree construction

Question

I'm trying to create an AST using ANTLR tree grammar.

Given a syntax like following:

rule    : head ':-' litlist (';' ':-' litlist)* DOT_END

I want to create a tree like following

 ^(RULES ^(head litlist)+)

That is, I want (head litlist) to be repeated as many as the number of litlist in the syntax. I tried something like above, but I'm getting an error like this:

Syntax error:required (...)+ loop did not match anything at input EXPR where EXPR is another term in the grammar.

Basically I want something like following:

a : type ID (',' ID)* ';' -> ^(type ID)+;

which is described in Tree constructon .

But my syntax has multiple tokens inside repeated clause, which seems to be a problem.

What is the right way to do this?

Answer 1

Have you tried another level of indirection? Such as:

rule    : clauses DOT_END ->  ^(RULES clauses)
clauses : head ':-' litlist (';' ':-' litlist)* -> ^(head litlist)+

Maybe the syntax is not proper yet.