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:Re: macro flow from inside to outside

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Peter Seibel wrote:

> that didn't just throw away those valuse. Here' a version that uses
> lexical variables, as requested. However it suffers from only allowing
> a finite number of named bags. There may be some clever way to work
> around that without walking the code. Or you could just live with it,
> the same way we live with other limits such as the number of arguments
> we can pass to a function.
> 
>   (defmacro bag (&body body)
>     (let ((bag (gensym))
>           (namedbags (loop repeat 10 collect (gensym))))
>       `(let ((,bag ())
>              ,@(loop for bag in namedbags collect `(,bag ())))
>          (flet ((find-bag (name)
>                   (cond
>                     (name
>                      (loop for bag in ',namedbags
>                         for bagname = (get bag 'bag-name)
>                         when (eql name bagname) return bag
>                         when (not bagname) do
>                           (setf (get bag 'bag-name) name) and
>                         return bag
>                         finally (error "Out of bags")))
>                     (t ',bag))))
>            (macrolet ((containing (item &optional name)
>                         `(push ,item ,(find-bag name)))
>                       (the-bag (name)
>                         (find-bag name)))
>              ,@body)
>            ,bag))))
> 
> This lets you write stuff like:
> 
>   CL-USER> (bag
>              (dotimes (i 10)
>                (if (evenp i)
>                  (containing i evens)
>                  (containing i odds)))
>              (containing (the-bag evens))
>              (containing (the-bag odds)))
>   ((9 7 5 3 1) (8 6 4 2 0))

Ruby:

(0..9).partition &:odd?
 ===>
[[1, 3, 5, 7, 9], [0, 2, 4, 6, 8]]


10.times.partition &:odd?
 ===>
[[1, 3, 5, 7, 9], [0, 2, 4, 6, 8]]


How would this be coded in Forth?
Is it even possible?

It seems that ANS Forth isn't used for real programming;
it's just used for doing a little arithmetic.


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:Re: macro flow from inside to outside "Robert L." <No_spamming@noWhere_7073.org> - 2016-11-29 09:40 +0000

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