[antlr-interest] String Templates and return values

[Michael Bedward]

Hi Andreas,

The problem is that when using template output the generated code for
your ArrayList will look like this...

list_exprs.add(exprs.getTemplate());

ie. it is a list of *templates* not a list of rule return scopes.

One way to get around this is to do something like the following...

In your token parser grammar...

funcCall : ID '(' expressionList ')' -> ^(FUNC_CALL ID expressionList) ;

expressionList : (expression (',' expression)* )? -> ^(EXPR_LIST expression*);

Then in your tree walker grammer...

expressionList returns [List list]
@init { $list = new ArrayList(); }
        : ^(EXPR_LIST ( e = expression {$list.add($e);} )
        ;

funcCall : ^(FUNC_CALL ID expressionList)
             {
                 for (Object o : $expressionList.list) {
                     // do stuff
                 }
             }
             ;

Hope this helps.
Michael


On 16 March 2011 08:15, Andreas Stefik <stefika at gmail.com> wrote:
> Hello all,
>
> My team is changing over our existing grammars from
> Parser->TreeWalker, to adding a new phase where we are outputting text
> from String templates. We have made some test grammars, which work
> fine, generating some output, but are having some difficulty
> integrating templates into our real system. Specifically, we started
> out doing the simplest thing, putting output = template; into the
> options. After changing around some of our grammar to account for
> different return types from outputting templates, we ran into one
> grammar rule that we haven't quite figured out how to fix:
>
> ^(FUNCTION_CALL qualified_name(COLON ID)? LEFT_PAREN ({temp++;}exprs
> += expression (COMMA exprs += expression)*)? RIGHT_PAREN)
>
> Inside the semantic action for this rule is the following:
>
> if($exprs != null) {
>                        for(Object o : $exprs) {
>                                expression_return ex = (expression_return)o;
>                                types.add(ex.eval.getType());
>                                argumentTypes.add(ex.eval.getType());
>                                steps.add(ex.step);
>                                values.add(ex.eval);
>                                registers.add(ex.eval.getRegister());
>                        }
>                }
>
> Basically, we are adding expressions into an ArrayList (exprs +=
> expression), which we then crawl through to grab details for the
> parameters. However, when we comment out output=template; this code
> works just fine, but when we leave it in, the array list is populated
> with null values. I don't quite understand what is going on here. For
> example, the code generated for the expression return looks about the
> same:
>
> //templating on
> public static class expression_return extends TreeRuleReturnScope {
>        public ExpressionValue eval;
>        public ExecutionStep step;
>        public StringTemplate st;
>        public Object getTemplate() { return st; }
>        public String toString() { return st==null?null:st.toString(); }
>    };
>
> as opposed to
>
> //templating off
> public static class expression_return extends TreeRuleReturnScope {
>        public ExpressionValue eval;
>        public ExecutionStep step;
>    };
>
> I assume that, perhaps, there is some other way should be doing this. Any clues?
>
> Stefik
>
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