Well, using code that I haven't touched in ages and a completely experimental approach, what I get for http://codepad.org/EvnKQm98 is:
case 1: doesn't do anything, doesn't loop case 2: behaves like S -> a case 3: segfault.. hrmmmm. case 4: reads in aaa. This is using http://projects.ioreader.com/cp/ Best Regards, Peter Goodman, http://www.petergoodman.me 65 High Park Ave. APT 413, Toronto, Ontario M6P 2R7 On Sun, Oct 9, 2011 at 4:39 PM, Bryan Ford <bryan.f...@yale.edu> wrote: > Left recursion in PEGs indeed seems like an interesting can of worms. For > those interested, I'm wondering how a few example grammars behave under your > preferred left-recursive parsing technique, and how you think they should > behave. > > First, a trivially evil left-recursive grammar: > > S <- S > > For example, does your parser detect and reject this somehow, or does it > behave the same as 'S <- f'? (I hope it doesn't result in an infinite loop > at runtime anyway. :) ) > > Now a grammar that's weird, not necessarily evil, in a slightly more subtle > way: > > S <- S / a > > Does this behave the same as 'S <- a', or do something else? How should it > behave? > > Cranking up the evilness factor one notch with a mutually left-recursive > grammar… > > S <- T / a > T <- S / &a > > Given the input string "a", does this behave the same as 'S <- a' (succeeding > and consuming) or the same as 'S <- &a' (succeeding but consuming no input)? > Do S and T behave the same way or differently? Should they? > > Now, another grammar that's not necessarily evil but strange in a slightly > different way: > > S <- Saa / a / > > Given the input string 'aaaa', for example, does/should this grammar consume > just 3 or all 4 a's, or does it do something else? What should it do? > > Cheers, > Bryan > _______________________________________________ > PEG mailing list > PEG@lists.csail.mit.edu > https://lists.csail.mit.edu/mailman/listinfo/peg > _______________________________________________ PEG mailing list PEG@lists.csail.mit.edu https://lists.csail.mit.edu/mailman/listinfo/peg
