> { $item[1] || $item[3] } but that would not work as the parser would
These two variables hold the TEXT that was matched by the appropriate rule.
What you need to do is maintain a symbol table. (A hash, I believe you
already have that). Then when you have a statement like
(b|c)
you would return
{$return = $symbols{$item[1]} || $symbols{$item[2]}; 1;}
The 1 is there only because I'm not really sure what your doing (I admit I
didn't read your code that closely) and it ensure that the rule succeeds.
You could avoid it if you knew for sure that $symbols{$item[1]} and [2] as
well would return defined values.
Actually on that note you might do something like this:
(assuming that there is a declaration phase in your language, oh and this
UNTESTED code in particular I cant remember if im using <error> correctly,
check the docs.)
my $grammar=<<'GRAMMER';
{
# Init code for grammar... Handles a symbol table
my %symbols;
sub symbol_add{
my $symbol=shift;
my $value =shift;
if ($symbols{$symbol}) {
warn "Attempt to declare $symbol more than once\n";
return undef;
}
$symbols{$symbol}=$value;
return $value
}
sub symbol_fetch{
my $symbol=shift;
unless (exists $symbols{$symbol}) {
warn "Attempt to fetch from undeclared $symbol\n";
return undef;
}
return $symbols{$symbol}
}
sub symbol_store{
my $symbol=shift;
my $value =shift;
unless (exists $symbols{$symbol}) {
warn "Attempt to store to an undeclared $symbol\n";
return undef;
}
$symbols{$symbol}=$value;
return $value
}
}
conjunction :l_identifier '|' r_identifier
{$return=symbol_fetch($item{l_identifier})||symbol_fetch($item{r_identifier}
)}
|<error>
declaration :'set' identifier '=' value
{$return=symbol_add($item{identifier},$item{value});}
| <error>
l_identifier:identifier {$return=$item[1]}
r_identifier:identifier {$return=$item[1]}
identifier :/[A-Za-z]+/
value :/\w+/
GRAMMER
BTW: This is basically how the red-dragon suggest one should handle
symbols, (with a perlish flavour)
HTH (even though it only addresses 1 line of your question)
Yves
