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Re: Generators (iterators) for Gnu Emacs

From: David Kastrup
Subject: Re: Generators (iterators) for Gnu Emacs
Date: Fri, 05 Dec 2014 10:54:58 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.0.50 (gnu/linux)

Stefan Monnier <address@hidden> writes:

>> (defmacro gen-make (&rest body)
>>   "Return a generator that evaluates BODY to generate elements.
>> For each call of `gen-next' with the the returned generator, BODY
>> will be evaluated to produce an element."
>>   (let ((this-element (make-symbol "this-element")))
>>     `(let (,this-element)
>>        (lambda ()
> AFAICT this requires lexical-binding in the caller, so we might want to
> signal an error if lexical-binding is nil.

Uh what?  The whole point of the make-symbol abomination is to get a
symbol uniquely used by only one instance of the lambda function.  This
is _exactly_ in order to _not_ require lexical binding.

>>          (if (eq ,this-element 'gen-done)
>>              'gen-done
>>            (setq ,this-element (progn ,@body)))))))

With lexical binding, this would look something like

(defmacro gen-mane (&rest body)
  `(let (this-element)
    (lambda ()
      (if (eq this-element 'gen-done)
          (setq this-element (progn ,@body))))))

And one would be tempted to see whether this really needs to be a macro.

David Kastrup

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