[antlr-interest] String Templates and return values

[Michael Bedward]

Oops...

The tree walker action for expressionList should be:
{ $list.add(e); }

Rather than
{ $list.add($e); }

Sorry about that.

Michael

On 16 March 2011 12:51, Michael Bedward <michael.bedward at gmail.com> wrote:
> 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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>