Re: LL vs LR languages (not grammars)

A Johnstone wrote:
| We're looking at top down vs bottom up parsers with infinite
| lookahead. [...] are there any _languages_ which are
| inherently LR and not LL(oo)? (LL with infinite lookahead [...])


Jerry Leichter <leichter@smarts.com> writes:
>I'm not sure what L(oo) would be.


Judging by the crossposting, I suspect A Johnstone was talking about LL
parsers with backtracking, as is supported by PCCTS. An LL(1) parser with
backtracking would not have any difficulty with your example language


> L = { x^{2n}y^{2n} e, x^{2n+1}y^{2n+1} o}


because it could try the first (even) alternative, and then if that
failed it could backtrack and try the other (odd) one.


--
Fergus Henderson <fjh@cs.mu.oz.au>
WWW: <http://www.cs.mu.oz.au/~fjh>
PGP: finger fjh@128.250.37.3
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