[cfe-dev] extending C with Clang

[John McCall]

On Sep 2, 2010, at 11:08 PM, Abramo Bagnara wrote:

> Il 03/09/2010 00:12, John McCall ha scritto:
>> 
>> On Sep 2, 2010, at 3:01 PM, Wei Li wrote:
>> 
>>> Dear All:
>>> 
>>> I am  extending C language for my research work and using Clang for
>>> this. I am adding some annotations which are not part of C language
>>> but will be helpful for my specific work.
>>> 
>>> Now consider the following:
>>> 
>>> int  foo() { return 1; }
>>> 
>>> is a legal  expression in C and is acceptable by the Clang. Now if I
>>> introduce a new annotation say "Wei"  and write the above expression
>>> as
>>> 
>>> int foo() Wei { return 1;}
>>> 
>>> I have to make changes in Clang at the front end to make it work. I
>>> see my extension as super set of C. That is my work should accept the
>>> legal C program as well.
>>> 
>>> Now here is the problem. When I make changes in the Clang . It accepts
>>> the new annotation but breaks the C programs. My understanding is that
>>> as I am adding to C so if my stuff works, any legal C  program should
>>> also work. But its not happening. I am not a compiler person. I am an
>>> engineer. Any suggestions? why clang is doing this or am I doing
>>> something    which is not compatible with the C grammar.?
>> 
>> Your parser modifications are probably broken.  I would strongly
>> suggest implementing Wei as a macro for __attribute__((Wei)) and then
>> just adding support for your new attribute.
> 
> Isn't a better idea for user that need this to have only one
> 
> __attribute__((custom(Expr)))
> 
> and store the Expr in the AST?

Why would this be better for users?  Easier to implement new annotations,
maybe, but easier for users?

Sean Hunt has done a lot of work to make it easy to add new attributes,
and more is forthcoming;  I would much prefer that over making a private
language of annotations expressed cumbersomely with expressions.

John.