I have the following in a grammar
rule TOP { ^ <statement>+ $ };
rule statement { <id> '=' <endvalue>
| { { self.panic($/, "Declaration syntax
incorrect") } }
};
rule endvalue { <keyword> '(' ~ ')' <pairlist>
| { self.panic($/, "Invalid declaration.") }
}
The grammar parses a correct input file up until the end of the file. At
that point even if there is no un-consumed input, there is an attempt to
match <id>, which fails. The failure causes the panic with 'Declaration
syntax'.
Am I missing something simple here?
I would have thought (though this is only a very newbie assumption)
that if the end of the input being sent to the grammar has been reached
after the last <statement> has been matched, then there should be no
reason for the parse method to try to match <statement> again, and if it
fails to test for the end of input.
Abstractly, it seems to me to be a bit like the difference between
testing for the truth of a condition before entering a loop, and testing
for the truth after the loop.
In trying to find a way out of this, I went looking for some information
about FAILGOAL. I could not find anything in the documentation or in the
specifications.
Google provided me with some conversations about FAILGOAL, but nothing
about how to use it. I do not know enough about the guts of Rakudo to
know where to look.
Would it be possible for someone who knows about this to add something
to the Documentation on Grammars?
(As I write this, I thought may be I need a lookahead pattern in the
TOP rule to ensure there is still input. But even so, that seems counter
intuitive.)
