Re: Programming language and IDE design

On Sun, 2 Mar 2014 00:03:18 +0000 (UTC), hu47121@usenet.kitty.sub.org
(Hannah) wrote:


>I don't think C++ is LL(2).
>
>Think e.g.
>
> T(a)++;
>vs.
> T(a)[5];
>
>(Example from n3485, page 131).
>
>The former is a statement, while the latter is a declaration, and you
>can decide this only very late. As the first four tokens are the same,
>C++ can't be LL(4), at least.
>
>As you can substitute '('^n x ')' ^n for a in this example (i.e. enclose
>that identifier in any number of parentheses), C++ isn't LL(n) for any n.
>(In the first case, "a" is a subexpression, that can be parenthesized,
>while in the second case, it's the declarator-id that can also be
>parenthesized).


I suppose that it depends on your definitions: a "syntax" token is
different from a "grammar" token ... a single grammar token can
represent an expression of any complexity. I think the whole notion
of lookahead is ambiguously level dependent.


But I concede your point re: syntax.


>So the C grammar is not LL(k) for any k, either. You can probably parse
>that particular part of the C/C++ grammar easily using LR.


However, both C and C++ are LL(*). LL(*) Antlr-3 grammars are
available for both http://www.antlr3.org/grammar/list.html


Also in that list you'll find an LL(k) Antlr-2 grammar for C/C++ which
at quick glance claims to be LL(2) ... but I haven't examined it to
know what tricks it may be employing.
http://hg.netbeans.org/main/file/tip/cnd.modelimpl/src/org/netbeans/modules/c
nd/modelimpl/parser/cppparser.g


George

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