18 Dec
2013
18 Dec
'13
7 p.m.
________________________________
De : moose-dev-bounces(a)iam.unibe.ch [moose-dev-bounces(a)iam.unibe.ch] de la part de Nicolas
Anquetil [Nicolas.Anquetil(a)inria.fr]
Date d'envoi : mercredi 18 décembre 2013 13:34
À : Moose-related development
Objet : [Moose-dev] Re: PetitParser PPCompositeParser, Infinite loop ?
On 12/18/2013 11:27 AM, Goubier Thierry wrote:
Le 18/12/2013 11:15, Nicolas Anquetil a écrit :
ben there is nothing magic about PPCompositeParser, it is a parser like
all the other one
and if you call rules without consuming any input + have a loop in the
rule calls, then there will be a infinite loop
Yes and no. Some parsers can't handle left-recursion in rules (petit parser? LL
parsers can't), some parsers don't have any problem with left recursion (LR
parsers like SmaCC).
I meant PPCompositeParser within PetitParser
All parsers PPParsers behave more or less the same way when we come to this.
If other can't handle correctly left-recursion ther eis no reasonnable reason to hope
that PPCompositeParser composite parser will do.
Ok, now I understand what you meant
Moreover, being a recursive descent parser, PetitParser naturally can't handle left
recursivity
You have a point :)
In this case, you will need to convert the grammar to a right recursive one, for example
like this (which is more or less the same thing I believe):
ClassOrInterfaceType: ClassType "/ InterfaceType -- this option is useless here as
it is equal to ClassType"
ClassType: TypeDeclSpecifier
TypeDeclSpecifier: TypeName { . TypeDeclSpecifier }
TypeName: Identifier TypeArgumentsopt
InterfaceType: TypeDeclSpecifier, TypeArgumentsopt
Some of the rules are not really needed, but that way it sticks closer to the reference
grammar
In that particular problem (InterfaceType = ClassType), PetitParser would select the first
alternative everytime, since they are both equal, and would never reach InterfaceType ?
Regards,
Thierry
nicolas
--
Nicolas Anquetil -- RMod research team (Inria)