Re: [Chicken-hackers] cond-expand and macros

[Kon Lovett]

On Nov 19, 2009, at 4:45 PM, Thomas Bushnell BSG wrote:

> Ok, so this is too weird by half.
>
> When I do (register-feature! 'foo), then the feature that is  
> registered
> is foo:, despite what the actual manual says.  And then, for some
> baroque reason, cond-expand matches foo and foo: (even though there is
> no "foo" feature registered, since it's actually foo:) and then,  
> inside
> the context of a syntax-rules, suddenly cond-expand *doesn't* match  
> foo,
> though it still matches foo:.
>
> Can I cry foul?  Why doesn't register-feature! simply register the
> feature specified without this on-again-off-again colon magic?  What  
> is
> the point of adding a colon in the first place to the symbol name?   
> Why
> is it magically removed again sometimes?

Features are converted to keywords. The colon suffix is just the  
default read/print form; #:keyword is the context-independent form.

'cond-expand' uses a function that ensures the tested symbol is a  
keyword, so 'foo' & '#:foo' are legal.

That the expansion-environment of a 'syntax-rules' transformer doesn't  
recognize 'cond-expand' is a different problem. (Note that 'syntax- 
rules' in Chicken 3 is not a core expander.)

> Thomas
>
>
> On Thu, 2009-11-19 at 19:27 -0500, John Cowan wrote:
> > Thomas Bushnell BSG scripsit:
> >
> > > The following code does not work:
> > >
> > > (define-syntax foo
> > >  (syntax-rules ()
> > >    ((_)
> > >     (cond-expand
> > >      (chicken (display "all good\n"))))))
> > > (foo)
> >
> > Calling (features) shows that the feature name is "chicken:", not
> > "chicken".  If you change the above to reference chicken:, all is  
> > well.
> > This is not backward compatible and is still probably a bug, but at
> > least it's a simple bug.
> >
> > On the other hand, (cond-expand (chicken (display "all good\n")))  
> > does
> > output "all good" right away.
>
>
>
>
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Best Wishes,
Kon