in reply to Where does $4 come from here?

What 3 elements? I'm completely guessing, but maybe its cause GRAMPROG expands to 
$1       $2    $3        $4       $5      ...                  
%token <ival> GRAMPROG GRAMEXPR GRAMBLOCK GRAMBARESTMT  ...
or
                  $1       $2    $3        $4

[download]
I just stumbled upon Perl 5 Internals by Simon Cozens which talks a bit this in Chapter 5. The Lexer and the Parser

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Re^2: Where does $4 come from here?
by PerlOnTheWay (Monk) on Jul 27, 2011 at 07:59 UTC
    My understanding is that:

    $1 $2 $3 supposed to refer to the 3 elements on the right of the production.

    While $$ refer to the LHS of the production. But in this production, there're only 3 elements on the right hand side, and I don't see what $4 refers to...
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      But in this production, there're only 3 elements on the right hand side, and I don't see what $4 refers to...

      Ok, here is more guessing, if we're talking about GRAMPROG  remember stmtseq and 

      
remember: /* NULL */ /* start a full lexical scope */
{ $$ = block_start(TRUE); }
;

stmtseq : /* NULL */
{ $$ = (OP*)NULL; }
| stmtseq fullstmt
{ $$ = op_append_list(OP_LINESEQ, $1, $2);
PL_pad_reset_pending = TRUE;
if ($1 && $2)
PL_hints |= HINT_BLOCK_SCOPE;
}
;

      [download]
      then surely $$ = op_append_list(OP_LINESEQ, $1, $2); becomes $2, $3, $4, right?

      :)

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[d/l]
[select]

        No, that's not how yacc works AFAIK...

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