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Re: procedure-source availability

From: Panicz Maciej Godek
Subject: Re: procedure-source availability
Date: Mon, 8 Oct 2012 22:11:59 +0200


>> Yes, you're right.
>> I even went a little further with that and now I also capture lexical
>> environment:
>> (use-modules (system syntax) (ice-9 local-eval))
>> (define-macro (function args . body)
>>   `(let ((environment (the-environment))
>>          (lexical-names (lexical-names))
>>          (procedure (lambda ,args ,@body)))
>>      (set-procedure-property! procedure 'source '(function ,args ,@body))
>>      (set-procedure-property! procedure 'environment environment)
>>      (set-procedure-property! procedure 'lexical-names lexical-names)
>>      procedure))
>> (where ``lexical-names'' returns the car-s of ``lexicals'', as defined
>> at the bottom of
>> )
>> So in addition to the source of the procedure, the lexical environment
>> can also be retrieved:
>> (define (procedure-lexicals proc)
>>   (map (lambda(symbol)
>>          (cons symbol
>>                (local-eval symbol (procedure-property proc 'environment))))
>>    (procedure-property proc 'lexical-names)))
> I don’t want to sound too dogmatic, but I think you really don’t want to
> take that route.  ;-)
> The issues with ‘local-eval’ have been discussed at length a year ago or
> so on guile-devel.  Basically, the problem is that it plays badly with
> compilation, and there are usually nicer way to achieve what you want.

Fortunately, calling local-eval isn't strictly necessary, as long as
the exciting and powerful `lexicals' macro is allowed. Then, the
`function' macro can be defined easily as:

(define-syntax function
  (lambda (x)
    (syntax-case x ()
      ((function args body ...)
       #'(let ((procedure (lambda args body ...))
               (get-lexicals (lambda()(lexicals function))))
           (set-procedure-property! procedure 'source '(function args body ...))
           (set-procedure-property! procedure 'get-lexicals get-lexicals)

(define (procedure-lexicals proc)
  ((procedure-property proc 'get-lexicals)))

I don't fully understand why it works, as syntax-case is still a
mystery to me, but I wrote it and it works perfectly, not to mention
that the expanded code is much cleaner now, without the-environment.

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