Re: [Chicken-users] miscmacros hygienic

[Kon Lovett]

On May 28, 2008, at 8:33 PM, Jim Ursetto wrote:

Thank you Jim for your recent life on the bleeding edge. (And Felix  
for expanding space.) I haven't visited yet so anything I say is  
subject to ignorance.

> I ported miscmacros (attached) to the hygienic branch and had a couple
> questions.
>
> First, is anyone using miscmacros?  I was wondering about the  
> following
> proposed change to the anaphoric macros:
>
> Current             -> Proposed
> (if* x y z)         -> (if* (it x) y z)
> (while* test body)  -> (while* (it test) body)
> (repeat* test body) -> (repeat* (it test) body)
>
> I think it's nicer not to break hygiene by introducing a hidden 'it'
> identifier--like dotimes does not.  In the port I actually  
> implemented them
> both ways; you just have to uncomment the desired behavior.  Thoughts?

I use the "anaphoric" forms but not "in anger." Yeah, the above is  
more Scheme-ish but I suggest leaving "it." Perhaps:

(if/let (it x) y z)
(while/let (it test) body)
...

or

(let/if (it x) y z)
(let/while (it test) body)
...

> Also--the miscmacros module uses a few bindings from the chicken  
> module:
>
> (import (only chicken
>              when unless handle-exceptions
>              let-optionals make-parameter))
>
> However adding this import line to miscmacros is basically useless  
> (as far as I
> can tell) because the macros are expanded in the caller's  
> environment, so the
> caller is the one who needs to do the import from chicken.
>
> I'd like to know the proper way to handle this, if any.  Does the  
> caller
> need to explicitly import any dependencies?

I hope not. Ahh, the return of the transitive monster.

That will be unworkable for the user.

> Similarly, as while* actually expands into an invocation of if*, it  
> does
> not work for the caller to do (import (only miscmacros while*)), as  
> the
> if* in the resulting expansion of while* will be undefined.

So dependencies are not automatically imported? Hum, "hoisted by ..."  
comes to mind.

> In fact the following doesn't look hygienic at all:
>
>  #;1> (module foo ()
>    (import scheme (only miscmacros while*))
>    (define-syntax if*
>      (lambda (f r c) (error 'bad)))
>    (while* (it (> 0 5)) (display it)))
>
>  Error: during expansion of (if*1305 ...) - bad
>
> Is this a bug or am I just confused?

Should a user module (program?) local definition, syntax or not,  
override the dependent definitions in an imported form? Good question.

<snip>

Best Wishes,
Kon