Infinite loop.

[philippesigaud]

Infinite loop.

[PhilippeSigaud]

On Wed, May 30, 2012 at 3:43 AM, meh.
[email protected]
wrote:

import std.stdio : writeln;
import pegged.grammar;

mixin(grammar(`
Test:
       A <- B*
       B <- .*
`));

void main () {
       writeln(Test.A.parse("lol"));
}

This is the reduced testcase for the culprit in my grammar.

The first invocation of B consumes lol and then stops.
The second invocation of B consumes nothing (nothing left), succeeds,
and the stops.
The third, ...

That's because .* can succeed while consuming nothing and you put it
into repetition.

I recently added checkGrammar just for that. Try:

void main () {
writeln(checkGrammar(Test:        A <- B*        B <- .*);
}

It should print a diagnostic saying B might consume nothing and A can
be an infinite loop.

test

Arg, it fails. Damn, it worked quite well last week, I tested it with
all kind of grammars, from JSON to C to D.

[meh]

But shouldn't it stop when there's nothing left to consume?

I'm adding the checkGrammar thing to peggeden, how should I pretty print the Diagnostic object?

[PhilippeSigaud]

On Wed, May 30, 2012 at 6:49 AM, meh.
[email protected]
wrote:

But shouldn't it stop when there's nothing left to consume?

By definition, .* can succeed on an empty string. Use .+ if you
want it to fail at the end.
Or:

EOI / .*

[PhilippeSigaud]

I added an introspection module. I'll add diagnoctics while generating the grammar.