If you use the rewrite option, it remains possible to write a precedenced statement that is inherently ambiguous. Rewriting is to prevent the *implementation* of precedenced rules from *introducing* new ambiguities not actually in the precedenced rule itself.
On Fri, Sep 2, 2016 at 1:30 PM, <[email protected]> wrote: > The rewrite approach seems to work great for recursive rules, but it > doesn't do anything for non-recursive rules. Running the following gives > me an ambiguous parse. Since opt1a is a higher priority, I expect to see > two productions of opt1a with no ambiguity. Am I expecting too much here? > Thanks for your help! > > > use strict; > use Marpa::R2; > use Data::Dumper; > > my $grammar = " > options ::= option* > option ::= opt1a || opt2a > opt1a ::= 'a' > opt2a ::= 'a' 'a' > > :discard ~ whitespace > whitespace ~ [\\s]+ > "; > > my $grammar = Marpa::R2::Scanless::G->new( { source => \$grammar } ); > my $input = 'a a'; > my $value_ref = $grammar->parse( \$input ); > > my $value = ${$value_ref}; > print "Output:\n".Dumper($value); > > > On Wednesday, August 31, 2016 at 8:55:21 PM UTC-6, Jeffrey Kegler wrote: >> >> I've remembered a major reason for preferring the rewrite approach. If >> you parse then rank, you're using ambiguous parsing -- Marpa is cool with >> that, but it is not necessarily as fast as an unambiguous parse. If the >> expression is of size X the parse could be as bad as O(X^3) and that can >> make a difference if you have a lot of long expressions. >> >> <snip> >> >> -- > You received this message because you are subscribed to the Google Groups > "marpa parser" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "marpa parser" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
