How difference of implement pragma handler in lexer and parser

[Pisit Makpaisit]

I notice that clang can implement the pragma handler in both lexer (Lex/Pragma.cpp) and parser (Parse/ParsePragma.cpp). How difference of they?

If my pragma directive has an expression. How can I parse and check expression syntax in pragma? 

I think I should implement pragma handler in parser for parse the expression but I don't know how can I do.

Thanks in advance. 
--
Remixman (Pisit Makpaisit)

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[Douglas Gregor]

On Jun 28, 2010, at 6:46 PM, Pisit Makpaisit wrote:

> I notice that clang can implement the pragma handler in both lexer (Lex/Pragma.cpp) and parser (Parse/ParsePragma.cpp). How difference of they?
>
> If my pragma directive has an expression. How can I parse and check expression syntax in pragma?
> I think I should implement pragma handler in parser for parse the expression but I don't know how can I do.

If you want to parse an expression in your pragma, you'll need to implement your pragma's parsing logic within the parser itself, which knows how to parse an expression.

        - Doug
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[Pisit Makpaisit]

Thank you.

Can I build and add node to AST in pragma's parsing?

--
Remixman (Pisit Makpaisit)

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[Douglas Gregor]

On Jun 29, 2010, at 6:09 PM, Pisit Makpaisit wrote:

> Thank you.
>
> Can I build and add node to AST in pragma's parsing?

Yes. The parser can make calls through the Action interface to Sema, which constructs the AST.

        - Doug


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