Re: Accessing values from a multiple subrule repeition

Given this:

   SimpleExpression : term (AddOperator term )(s?)

$item[1] relates to the first "term".

$item[2] relates to the "(AddOperator term )(s?)".  So, $item[2] is an arrayref 
of the last element of "AddOperator term" (i.e. "term").  As is, there's no way 
to grab the "AddOperator" values.  In fact, this is equivalent to writing two rules:

   pair             : AddOperator term
   SimpleExpression : term pair(s?)

The solution is to append an element to end of the "AddOperator term" that 
evaluates to an expression from which you can obtain "AddOperator" and "term". 
This will do:

   pair             : AddOperator term { [@item[1,2]] }
   SimpleExpression : term pair(s?)

You can also express this as a single rule due to the lexical scoping on @item:

   SimpleExpression : term (AddOperator term { [@item[1,2]] })(s?)

Now, $item[2] is an arrayref of arrayrefs containing both AddOperator and term.

However, you might want to take a look at the <leftop: ...> directive, which 
provides a more convenient syntax for this common idiom:

   SimpleExpression : <leftop: term AddOperator term>

In fact, there's even a short-hand for the short-hand, and this may work for 
your application as well:

   SimpleExpression : term(s /[-+]/)

See the Parse::RecDescent POD in the section under "Specifying operations".

-davidm


PerlDiscuss - Perl Newsgroups and mailing lists wrote:
> With the following code fragment, I realise I can access the array
> containing the term values using the notation $item[2] as shown below:
> 
> SimpleExpression : term (AddOperator )(s?)
> {
> 	my $SimpleExpressionArray = $item[2];
> 	my @SimpleExpression =  @$SimpleExpressionArray;
> }
> 
> However, if I have repetition of multiple statements  such as (AddOperator
> term )(s?) as show below. How can I access both the AddOperator values,
> and the term values. If I access $item[2] as in the above example, it only
> contains the term rule values and the AddOperator values apear to be lost.
> 
> SimpleExpression : term (AddOperator term )(s?)
> {
> }
> 
> I apologise if I have not included enough detail, I have tried to be
> direct and to the point. Please let me know if you require more detail.
> 
> Paul Kennerley
>