Re: [sv-bc] Possible SV macro expansion algorithm

Hi Eric,

Coffin, Eric wrote:
> ... the ASCII representation of [macro] expansion is less important
> than the fact that it is merely [a sequence of] tokens.

The ASCII representation is only significant due to the `" feature that
captures macro argument text as the data of a string literal.

> C++ treats macro expansion as a text-to-token transformation.

Is your proposal (below) different from C++ pre-processing in
any major respect?

In the "... looking for identifiers matching formal argument names"
activity, there is an implied tokenization of the unexpanded body.
We need to specify the rules for that tokenization, in particular
whether escaped identifiers are to be recognized.

On first review, though, this looks a lot better than the existing
section (23.2 of 1800-2005)!

Greg


> 
> *********************************************************************
> 
> Here is a rough outline of a possible way to expand macros that might
> give some
> consistency to the various SV implementations out there.
> 
> Order of actions to expand a macro:
> 
>  - After the macro use has been identified in the SV source text,
>    gather the use's actual arguments.
> 
>  - Independently expand all actual arguments, but do not substitute
>    them into the macro body.  If the macro use did not specify an
>    actual and a default value was specified then expand the default
>    text.  Some SV implementations first expand and then substitute,
>    while others do not.  Note that all arguments should be expanded
>    even if they are not used within the macro body.
> 
>  - Walk through the macro body looking for identifiers matching
>    formal argument names.  Replace any macro formal argument with its
>    expanded actual text, unless the macro formal is adjacent to a
>    tick-tick ('').  If the formal arg is next to a tick-tick, then
>    literally substitute the (unexpanded) actual text for the formal arg.
> 
>  - do {
>      - Perform token-pasting upon the expansion's body.  Token
>        pasting should have no effect upon the `" and the `\`" macro
>        operators.  Furthermore, token pasting ignores any white space,
>        and will not paste comments, nor paste across comments.
>      - Rescan the resulting body for any more macros to expand.
>        Expand them.  Do not expand `" or `\`".
>      } while the expansion body changes
> 
>  - Expand the special macro-operators, tick-quote `" and
> tick-slash-tick-quote `\`"
> 
> -Eric
> 
> 
> 
> 
> 
> 


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