remprop

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ANSI Common Lisp 10 Symbols 10.2 Dictionary of Symbols

10.2.16 remprop Function

Syntax:

remprop symbol indicator generalized-boolean

Arguments and Values:

symbol - a symbol.

indicator - an object.

generalized-boolean - a generalized boolean.

Description:

remprop removes from the property list₂ of symbol a property₁ with a property indicator identical to indicator. If there are multiple properties₁ with the identical key, remprop only removes the first such property. remprop returns false if no such property was found, or true if a property was found.

The property indicator and the corresponding property value are removed in an undefined order by destructively splicing the property list. The permissible side-effects correspond to those permitted for remf, such that:

 (remprop x y) ==(remf (symbol-plist x) y)

Examples:

 (setq test (make-symbol "PSEUDO-PI")) #:PSEUDO-PI
 (symbol-plist test) ()
 (setf (get test 'constant) t) T
 (setf (get test 'approximation) 3.14) 3.14
 (setf (get test 'error-range) 'noticeable) NOTICEABLE
 (symbol-plist test) 
 (ERROR-RANGE NOTICEABLE APPROXIMATION 3.14 CONSTANT T)
 (setf (get test 'approximation) nil) NIL
 (symbol-plist test) 
 (ERROR-RANGE NOTICEABLE APPROXIMATION NIL CONSTANT T)
 (get test 'approximation) NIL
 (remprop test 'approximation) true
 (get test 'approximation) NIL
 (symbol-plist test)
 (ERROR-RANGE NOTICEABLE CONSTANT T)
 (remprop test 'approximation) NIL
 (symbol-plist test)
 (ERROR-RANGE NOTICEABLE CONSTANT T)
 (remprop test 'error-range) true
 (setf (get test 'approximation) 3) 3
 (symbol-plist test)
 (APPROXIMATION 3 CONSTANT T)

Side Effects:

The property list of symbol is modified.

Exceptional Situations:

Should signal an error of type type-error if symbol is not a symbol.

See Also:

remf, symbol-plist

Notes:

Numbers and characters are not recommended for use as indicators in portable code since remprop tests with eq rather than eql, and consequently the effect of using such indicators is implementation-dependent. Of course, if you've gotten as far as needing to remove such a property, you don't have much choice - the time to have been thinking about this was when you used setf of get to establish the property.

Allegro CL Implementation Details:

None.

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