As Parse::RecDescent gets its grammar as a string, I see no way to create clever closures or anything that will allow you to use lexical variables. One approach I can think of would be judicious use of local to isolate the effects, but that implies that your parsers won't call each other recursively:
...
sub do_parse {
local $parser_info = {
tokens => [],
};
my $p6 = Parse::RecDescent->new(q{
{
push @{ $parser_info->{tokens} }, $item{letter}
}
});
};
...
That way, you reduce your need for a global variable to one entry point, $parser_info. I think you can also instruct Parse::RecDescent to return you the whole parse tree as an AST instead of having it execute code immediately, by using the <autotree> directive. That wouldn't require any code within your parser, but you have to walk the tree yourself after it has been constructed.