Re: Macro vs Function

[Herbert Euler]

> From: David Kastrup <address@hidden>
> To: "Herbert Euler" <address@hidden>
> CC: address@hidden
> Subject: Re: Macro vs Function
> Date: Wed, 12 Apr 2006 18:59:45 +0200
>
> "Herbert Euler" <address@hidden> writes:
>
> >>From: David Kastrup <address@hidden>
> >>To: "Herbert Euler" <address@hidden>
> >>CC: address@hidden
> >>Subject: Re: Macro vs Function
> >>Date: Wed, 12 Apr 2006 17:29:40 +0200
> >>
> >>Why are you bothering with "apply" in the first place?  It does not
> >>look like you have any need for it.  Just write
> >
> > Because func is supposed to be a variable set by, for instance,
> >
> >    (setq f '+)
> >
> > And '+ is just for testing purpose.
>
> Could you _please_ quote the relevant definitions when answering?  It
> causes a lot of extra work if I have to go constantly to previous
> parts of the thread to dig them out.

I'm sorry.

> I still don't see why you can't just write
>
> (defmacro xgp-casi2-safe-call-iter (func largs)
>  (and largs
>      `(condition-case nil
>            (funcall ,func ,@(car largs))
>          (error (xgp-casi2-safe-call-iter ,func ,(cdr largs))))))
>
> Or, if you really insist on "apply",
>
> (defmacro xgp-casi2-safe-call-iter (func largs)
>  (and largs
>      `(condition-case nil
>            (apply ,func (list ,@(car largs)))
>          (error (xgp-casi2-safe-call-iter ,func ,(cdr largs))))))

Yes, these two both work.  When I wrote the "complete
and utter contorted mess":

> (defmacro xgp-casi2-safe-call-iter (func largs)
>   (if largs
>       `(condition-case nil
>            (apply ,func ,((lambda (a) `(quote ,(car a))) largs))
>          (error (xgp-casi2-safe-call-iter ,func ,(cdr largs))))
>     'nil))

I didn't understand the mechanism of macros.  If I'm writing
them now, I too will write simple ones like what Stuart D.
Herring and you write.

Thank you very much, for making me understand how macro
works.

Sincerely yours,
Guanpeng Xu

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