问题
In order to further my understanding of parsers and grammars, I'm searching for a (hopefully simple) example of a language that is LL(2) but not LL(1). That is, a language that can be generated by an LL(2) grammar but not by any LL(1) grammar.
Are there useful languages in that class ? I.e could we imagine a computer language that is LL(2) but not LL(1) ?
回答1:
Parsing Techniques by Grune and Jacobs presents an example. An older version of this book is available online at
http://dickgrune.com/Books/PTAPG_1st_Edition/BookBody.pdf
and the example is on page 181.
回答2:
The example mentioned in the book linked in Gunther's answer:
S -> a S A | epsilon
A -> a^k b S | c
is a grammar describing an LL(k+1) language that is not LL(k). In particular,
S -> a S A | epsilon
A -> a b S | c
is a grammar describing an LL(2) language that is not LL(1).
来源：https://stackoverflow.com/questions/10634197/ll2-language-that-is-not-ll1