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Re: Quotations revisited

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Marcel Hendrix wrote:

> mhx@iae.nl (Marcel Hendrix) wrote Re: Quotations revisited
> [..]
>> When [: and ;] switch to some private wordlist, EXIT and RECURSE can
>> be used instead of MY-EXIT and MYSELF. LOCALs are possible with a
>> little extra effort. Was there anything else people wanted?
> 
> Although a private set of locals doesn't work, accessing outer locals
> may work sufficiently close to what is intended:

In Gforth, you can rather have a private set of locals, no access to 
outer locals (i.e. no closures).

> However, Knuth's Man-or-Boy test fails for calldepths > 3. (At that
> point the locals stack is empty, so apparently the recursion is
> supposed to make copies?)

It's supposed to create a closure.  A closure contains both the function 
itself *and* the values of the locals at the time of its creation.  The 
livetime of a closure can exceed the livetime of its creating word:

: incrementer ( by-n -- xt ) { by-n } [: by-n + ;] ;
5 incrementer Alias 5+

If I would implement closures in Forth, I'd rather prefer a more 
explicit construction that lexical scoping.  My closures would look 
like:

: incrementer ( by-n -- xt ) [:{ by-n } by-n + ;] ;

What [:{ does at runtime:  It allocates a buffer for a structure similar 
to words defined by create does>, and the space for by-n, which is 
initialized from the stack.

-- 
Bernd Paysan
"If you want it done right, you have to do it yourself"
http://bernd-paysan.de/

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Re: Auotations revisited Andrew Haley <andrew29@littlepinkcloud.invalid> - 2012-07-15 03:45 -0500
  Re: Quotations revisited mhx@iae.nl (Marcel Hendrix) - 2012-07-15 12:52 +0200
    Re: Quotations revisited mhx@iae.nl (Marcel Hendrix) - 2012-07-15 16:08 +0200
      Re: Quotations revisited Bernd Paysan <bernd.paysan@gmx.de> - 2012-07-15 17:08 +0200

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