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Null object: Difference between revisions
Added EchoLisp
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<lang e>object == null</lang>
=={{header|EchoLisp}}==
The null object - '''null''' - is the same as the empty list (). It may be tested with the '''null?''' or '''!null?''' predicates. NB : null is not the same as the boolean #f (false). null evaluates to #t (true) in logical operations.
<lang lisp>
null → null
() → null
(null? 3) → #f
(!null? 4) → #t
(null? null) → #t
;; careful - null is not false :
(if null 'OUI 'NON) → OUI
;; usual usage : recursion on lists until (null? list)
(define (f list)
(when (!null? list)
(write (first list)) (f (rest list))))
(f '( a b c)) → a b c
</lang>
=={{header|Eiffel}}==
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