Re: [PATCH] More %define/%code encapsulation

[Paolo Bonzini]

> > This patch defines the conditional macros for %define and %code.
>
> Just out of curiosity, are you actually using all these new macros, or are 
> you just anticipating that someone might find them useful?

I'm mostly anticipating the need, but I have use cases.

- for _if, I have "%define single_class" in Java if you want lexer and 
parser to reside in the same class.  And actually it would be better to 
extend it to accept "true" or "false" too, hence the _case.

- for _ifval, I'm thinking of

m4_define([b4_class_name], [b4_get_percent_code([package])dnl
b4_get_percent_code_ifval([package], [.])$1])

> I ended up not adding the _ifdef's in my previous patch because I wasn't 
> sure what I'd ever use them for.  Thinking about it now, I guess some 
> skeletons might want to require certain %define's or %code's and 
> warn/complain when the grammar doesn't define them.  Is that what you're 
> thinking?  Anything else?

- for _ifdef, that's it.

- for _case, I'm thinking of a multi-value flag.

> > +# b4_percent_define_ifdef(VARIABLE, IF-TRUE, IF-FALSE)
> > +# ----------------------------------------------------
> > +# If the %define variable VARIABLE is defined, expand IF-TRUE, else expand
> > +# IF-EMPTY.  Also, record the skeleton's usage of VARIABLE by defining
>
> s/IF-EMPTY/IF-FALSE/

Yes, my bad.

> > +# b4_percent_define_if(VARIABLE, IF-TRUE, IF-FALSE)
> > +# -------------------------------------------------
> > +# If the %define variable VARIABLE is defined to anything but 0, evaluate 
> > IF-TRUE.
> > +# If it is defined to 0, evaluate IF-FALSE.
>
> In my experience, an empty string also means false.

Except that I wanted to make the default of %define become empty rather 
than 1 in a follow-up patch (disconnected from the Java skeleton).

> > +# b4_percent_define_case(VARIABLE, [VALUE1, THEN1]..., ELSE)
> > +# ----------------------------------------------------------
> > +# If the %define variable VARIABLE is defined to VALUE1, evaluate THEN1, and
> > +# so on.  If none of the values match, expaand ELSE.
>
> Isn't the ELSE argument optional?  In the other macros, isn't IF-FALSE 
> optional?

Right.

Paolo