Re: C++ Grammar - Update

Mike Dimmick wrote:
>
> The major reported problem with the C++ syntax is that it requires
> semantic information to parse correctly. This isn't strictly true,
> one can follow the technique of Ed Willink
> (http://www.computing.surrey.ac.uk/research/dsrg/fog/FogThesis.html)
> who uses purely syntactic methods. However, this technique needs a
> lot of subsequent analysis to correct the misparsed syntax trees, and
> requires backtracking, and also needs some complicated binary-search
> methods to resolve template usage into a consistent AST. [2] I
> therefore decided to stick with the classic method of producing a
> symbol table "on the fly" as it were.


I believe some C++ constructs require semantic lookup. Take, for
example (in namespace scope),


    A B (C);


What is this?


I recently ran into this problem while creating a tool called lzz.
lzz is a C++ preparser: it generates a header and source file from a
file containing a sequence of C++ declarations. lzz can significantly
reduce coding time. The tool is still in its beta stage, although it
is being used successfully on a project. For more information see
http://www.lazycplusplus.com.


I'm using a backtracking LR(1) parser without a symbol table.
Luckily, I do not have to parse function bodies and expressions--the
(context dependent) lexer passes this code to the parser as single
tokens. Outside of function bodies and expressions lzz only has four
restrictions:


  o parameters must be named in function types


  o parameters must be named in the catch clause of function try blocks


  o parameters must be named in template declarations


  o "_dinit" must precede direct initializers


Only the last restriction isn't C++ code. Alternatively, I could have
required expressions in a direct initializer to be enclosed within a
redundant set of parenthesis (but I find typing "_dinit" is often
easier).


Mike

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