FOOP Scoop

[m i c h a e l]

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 '... '...)


;-)

[itistoday]

Thanks!  What little treasures I find while leisurely browsing the newLISP forum instead of learning Cocoa...