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

[Jon Awbrey]

o~~~~~~~~~o~~~~~~~~~o~~~~~~~~~o~~~~~~~~~o~~~~~~~~~o

TOP.  Commentary Note 23

o~~~~~~~~~o~~~~~~~~~o~~~~~~~~~o~~~~~~~~~o~~~~~~~~~o

Pinch.

Pinch is a transformation of ideas that operates on the
assumption that its argument idea references a form in a
cycle of forms.  In such a setting it acts as the identity
on the argument idea but has the side-effect of isolating
the referent form and detaching it from its encyclement.
As usual, Pinch observes the rule "Nil In, Nil Out".

In this context 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 argument idea and
pinch (this) is the constructed result:

Before:  o---------------------------------o
         |   o-----o   o-----o   o-----o   |
         o-->| a 1 |-->| b 2 |-->| c 3 |---o
             o-----o   o-----o   o-----o
                          ^
                     this |
                          @

After:   o---------------------------------o
         |   o-----o             o-----o   |
         o-->| a 1 |------------>| c 3 |---o
             o-----o             o-----o

                   o-------------o
                   |   o-----o   |
                   o-->| b 2 |---o
                       o-----o
                          ^
             pinch (this) |
                          @

function pinch (this: idea): idea;
var here, there: idea;
begin
 here := nil;
 if this <> nil then
  begin
   there := beset (fore (this), next (this));
   here := cog (this)
  end;
 pinch := here
end;

o~~~~~~~~~o~~~~~~~~~o~~~~~~~~~o~~~~~~~~~o~~~~~~~~~o
inquiry e-lab: http://stderr.org/pipermail/inquiry/
o~~~~~~~~~o~~~~~~~~~o~~~~~~~~~o~~~~~~~~~o~~~~~~~~~o