[Inquiry] Re: Theme One Program -- Commentary -- Fore

[Jon Awbrey]

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TOP.  Commentary Note 21

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Fore.

Fore is a transformation of ideas that operates on the
assumption that its argument idea references a form in
a cycle of forms.  Its functional value is the address
of the form that is immediately prior to this referent
form, as determined by the cyclic ordering in question.

In this setting a "cycle of forms" will always refer to a "by-cycle of forms",
that is, a finite set of forms that are linked by way of their 'by' addresses,
as illustrated in the following figure, where 'this' is the intended argument
and fore (this) is the computed result:

 o-------------------------------------------------o
 |   o-----o   o-----o         o-----o   o-----o   |
 o-->|     |-->|     |-->···-->|     |-->|     |---o
     o-----o   o-----o         o-----o   o-----o
     ^                                   ^
this |                                   | fore (this)
     @                                   @

function fore (this: idea): idea;
var here: idea;
begin
 here := nil;
 if this <> nil then
  begin
   here := this;
   repeat here := next (here)
    until next (here) = this
  end;
 fore := here
end;

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