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newLISP Fan Club

Forum => Anything else we might add? => Topic started by: m i c h a e l on February 04, 2008, 04:49:11 PM

Title: FOOP Scoop
Post by: m i c h a e l on February 04, 2008, 04:49:11 PM
FOOP Scoop!



If this is the mother of all constructors:


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(define (Class:Class) (cons (context) (args)))


Then this must be the daddy of all predicates:


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(define (Class:? obj)
  (and (list? obj) (not (empty? obj)) (= (obj 0) (context)))
)


Of course, for this to have real meaning within the context of your code, you must use the fully qualified method name when applying it:


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> (Point:? (Point 23 54))
true
> (Complex:? (Complex 0.68 -1.64))
true
> (Complex:? (Point 0 0))
nil
> _


When using it this way, it's usually referred to as a class method.



The predicate's first two tests, (list? obj) and (not (empty? obj))), can become part of a function to test for objectness:


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(constant (global 'object?)
  (fn (obj)
     (and (list? obj) (not (empty? obj)) (context? (obj 0)))
  )
)


With that, you could define the predicate this way:


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(define (Class:? obj) (and (object? obj) (= (obj 0) (context))))


Even though these should be used as class methods, you can still apply the ? to an object using polymorphism:


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> (:? (Point 23 43))
true
> (:? (Complex 0.33 0.11))
true
> (:? (CornFlakes (CornFlake) (CornFlake) (CornFlake) ...))
true
> _


But in essence, all you're really asking the object is: are you your own type? :-)



m i c h a e l



P.S. Even the ellipsis in the CornFlakes object can become valid newLISP code:


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(set '... '...)


;-)
Title:
Post by: itistoday on February 05, 2008, 02:06:11 PM
Thanks!  What little treasures I find while leisurely browsing the newLISP forum instead of learning Cocoa...
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