Template construction - ANTLR 3

ANTLR v3 has built-in support for constructing StringTemplate templates. there are two forms: Special symbols in actions and rewrite rules similar to AST construction. I am including a number of rules from the mantra example.

Sometimes you just need a string to become a template:

'void' -> {%{"void"}}

The following tree grammar rule illustrates some of the basic rewrite rules:

primary
    :   ID -> {%{$ID.text}} // create template from token text

        // create template using rule results as template attributes
    |   ^('new' typename args=expressionList)
            -> new(type={$typename.st},args={$args.st})

    |   listliteral -> {$listliteral.st} // reuse template built for listliteral

        // create template using token text as template attribute
    |   NUM_INT   -> int_literal(v={$NUM_INT.text})
    ;

And here are some more complicated examples:

assignment
    :   // special case "a[i] = expr;"
        ^('=' ^(EXPR ^(INDEX a=expression i=expression)) rhs=completeExpression)
        -> indexed_assignment(list={$a.st}, index={$i.st}, rhs={$rhs.st})
    |   ^('=' lvalue completeExpression)
        -> assignment(
                lhs={$lvalue.st},
                rhs={$completeExpression.st})
    |   ^(assign_op lvalue completeExpression)
        -> assignment_with_op(
                type={$assign_op.start.type.name},
                op={$assign_op.text},
                lhs={$lvalue.st},
                rhs={$completeExpression.st})
    ;

When you need to append multiple strings or templates into a another template use the += operator for a rule's return value (former use of toTemplates no longer required). For example adding variable declarations inside a struct template :

structDeclaration
    :   name=Ident (decls+=typeDecls)+ -> structDecl(name={$name.text},declList={$decls});
    ;

and the templates for a struct declaration may be something like this :

structDecl(name,declList) ::= <<
struct <name> {
    <declList; separator="\n">
}

More on string templates can be found here: String Template