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  ANSI Common Lisp   5 Data and Control Flow   5.3 Dictionary of Data and Control Flow

5.3.36 equalp Function

equalp x y    generalized-boolean

Arguments and Values:
x - an object.

y - an object.

generalized-boolean - a generalized boolean.

Returns true if x and y are equal, or if they have components that are of the same type as each other and if those components are equalp; specifically, equalp returns true in the following cases:

equalp does not descend any objects other than the ones explicitly specified above. The next figure summarizes the information given in the previous list. In addition, the figure specifies the priority of the behavior of equalp, with upper entries taking priority over lower ones.

Summary and priorities of behavior of
Type Behavior
number uses =
character uses char-equal
cons descends
bit vector descends
string descends
pathname same as equal
structure descends, as described above
Other array descends
hash table descends, as described above
Other object uses eq

 (equalp 'a 'b)  false
 (equalp 'a 'a)  true
 (equalp 3 3)  true
 (equalp 3 3.0)  true
 (equalp 3.0 3.0)  true
 (equalp #c(3 -4) #c(3 -4))  true
 (equalp #c(3 -4.0) #c(3 -4))  true
 (equalp (cons 'a 'b) (cons 'a 'c))  false
 (equalp (cons 'a 'b) (cons 'a 'b))  true
 (equalp #\A #\A)  true
 (equalp #\A #\a)  true
 (equalp "Foo" "Foo")  true
 (equalp "Foo" (copy-seq "Foo"))  true
 (equalp "FOO" "foo")  true
 (setq array1 (make-array 6 :element-type 'integer
                            :initial-contents '(1 1 1 3 5 7))) 
 #(1 1 1 3 5 7)
 (setq array2 (make-array 8 :element-type 'integer
                            :initial-contents '(1 1 1 3 5 7 2 6)
                            :fill-pointer 6))
 #(1 1 1 3 5 7)
 (equalp array1 array2)  true
 (setq vector1 (vector 1 1 1 3 5 7))  #(1 1 1 3 5 7)
 (equalp array1 vector1)  true 

See Also:
eq, eql, equal, =, string=, string-equal, char=, char-equal

Object equality is not a concept for which there is a uniquely determined correct algorithm. The appropriateness of an equality predicate can be judged only in the context of the needs of some particular program. Although these functions take any type of argument and their names sound very generic, equal and equalp are not appropriate for every application.

Allegro CL Implementation Details:

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