[plt-scheme] macros that expand into top-level definitions with computed names

Thanks Matthias,

That certainly is a different approach than defmacro! But it does seem  
to get me most of the way there and I think I could get the rest of  
the way (and maybe understand and appreciate more of what I've been  
reading in the Macros section of the reference) if I could see how to  
modify your example so that it evaluated its first argument, as in:

(define partial-name "yours")

(def partial-name x (sqrt x))

(my-yours 4) => 2

BTW this isn't for prefixing or suffixing per se -- it's for a version  
of a stack based language in which there are a bunch of types, a bunch  
of instructions that work the same way on all types but with different  
names and accessing different stacks, and I want to generate functions  
by looping over the two lists and executing a definition for each type/ 
instruction pair. (These aren't PLT types, they're types in my  
language -- http://hampshire.edu/lspector/push.html -- and I'm not  
interested at the moment in doing this in any way that depends on PLT  
types... I just want to be able to generate and execute definitions  
with computed names and bodies, which is something I often find handy  
in CL.)

Thanks,

  -Lee

On Aug 11, 2009, at 10:27 PM, Matthias Felleisen wrote:

>
> Do you mean this kind of thing:
>
> #lang scheme
>
> (define-syntax (def stx)
>  (syntax-case stx ()
>    [(_ f x body ...)
>     (identifier? (syntax f))
>     (let* ([f:sym (syntax-e (syntax f))]
>            [my-f:str (string-append "my-" (symbol->string f:sym))]
>            [my-f:sym (string->symbol my-f:str)]
>            [my-f:id (datum->syntax stx my-f:sym)])
>       #`(define #,my-f:id (lambda (x) body ...)))]))
>
> (def yours x (sqrt x))
>
> (my-yours 4)
>
> I recommend creating a module in your personal collects that  
> provides for adding prefixes and suffixes and importing it when  
> needed. It's in my standard collection
>
> -- Matthias
>
>
>
> On Aug 11, 2009, at 9:31 PM, Lee Spector wrote:
>
>>
>> I'm still transitioning from Common Lisp (thanks for all of the  
>> pointers so far) and I'm having trouble doing something that I  
>> could easily do with a CL macro.
>>
>> I'd like to write a macro (or whatever) that takes two strings and  
>> defines a function named with the symbol formed from interning the  
>> concatenation of the strings. For example if the arguments have the  
>> values "my-" and "function" in a particular call then I'd like the  
>> effect of the call to be the same as something like (define my- 
>> function <more stuff here>).
>>
>> This is straightforward using defmacro in CL, but looking through  
>> the section of the PLT reference on macros I don't see where to  
>> start.  In CL if I didn't know about defmacro, and if I didn't mind  
>> having my definitions evaluated in a null lexical environment, then  
>> I could hack it with eval. So with my new (but still minimal)  
>> understanding of eval and namespaces in PLT I tried this:
>>
>> -------
>> #lang scheme
>>
>> (define-namespace-anchor nsa)
>> (define ns (namespace-anchor->namespace nsa))
>>
>> (eval `(define ,(string->symbol (string-append "my-" "function"))
>>              (lambda () 'runs))
>>      ns)
>>
>> (my-function)
>> -------
>>
>> This doesn't work -- expand: unbound identifier in module in: my- 
>> function -- although if I get rid of the call to my-function in the  
>> definitions pane then it does compile and allow me to call my- 
>> function (which then does the right thing) in the interactions  
>> pane. But that's not good enough for my purposes.
>>
>> Of course this hack with eval is probably the wrong approach anyway  
>> -- it would be a bad way to do it in CL and I'm guessing that a  
>> completely different approach would be appropriate in PLT. And I  
>> think I'm just not seeing the right part of the PLT docs because of  
>> the differences in terminology.
>>
>> Can someone point me in the right direction on this?
>>
>> Thanks,
>>
>> -Lee
>>
>> --
>> Lee Spector, Professor of Computer Science
>> School of Cognitive Science, Hampshire College
>> 893 West Street, Amherst, MA 01002-3359
>> lspector at hampshire.edu, http://hampshire.edu/lspector/
>> Phone: 413-559-5352, Fax: 413-559-5438
>>
>> Check out Genetic Programming and Evolvable Machines:
>> http://www.springer.com/10710 - http://gpemjournal.blogspot.com/
>>
>> _________________________________________________
>> For list-related administrative tasks:
>> http://list.cs.brown.edu/mailman/listinfo/plt-scheme

--
Lee Spector, Professor of Computer Science
School of Cognitive Science, Hampshire College
893 West Street, Amherst, MA 01002-3359
lspector at hampshire.edu, http://hampshire.edu/lspector/
Phone: 413-559-5352, Fax: 413-559-5438

Check out Genetic Programming and Evolvable Machines:
http://www.springer.com/10710 - http://gpemjournal.blogspot.com/