[antlr-interest] TreeParser: Qs about generated code

[Terence Parr]

On Saturday, May 17, 2003, at 07:24  AM, rustydstone wrote:

> Simple grammar:
>
> expr returns [Object o] {
> [...]
>
>     | #(UNARY_MINUS e:expr) {o = il.unaryMinus(e);}
> [...]
>     ;
>
> The respective generated TreeParser code looks like the following:
>
> 1  case UNARY_MINUS:
> 2   {
> 3        AST __t25 = _t;
> 4        AST tmp20_AST_in = (AST)_t;
> 5        match(_t,UNARY_MINUS);
> 6        _t = _t.getFirstChild();
> 7        e = _t==ASTNULL ? null : (AST)_t;
>    // I'd like to avoid the call on line 8 since I'm calculating the
>    // result myself on line 12
> 8        expr(_t);
> 9        _t = _retTree;
> 10       _t = __t25;
> 11       _t = _t.getNextSibling();
> 12       o = il.unaryMinus(e);
> 13       break;
> 14  }
>
> Questions:
> 1) I thought when I say "#(UNARY_MINUS e:expr)" instead of
> "#(UNARY_MINUS e=expr)", ANTL would not bother calculating expr (since
> the AST itself is requested, not the value of the expr).

If you say expr, ANTLR will parse it.  Say '.' and it will acknowledge 
that there is a child.

> Is there a
> way to tell ANTL that I will walk this part of the tree and calculate
> the result myself?
>
> 2) Lines 9, 10, 11 seem a bit strange. Not sure I understand the
> meaning of this.

Just parsing bookkeeping.

Ter

> Any ideas? Thanks
>
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