x—an object.
y—an object.
generalizedboolean—a generalized boolean.
Returns true if x and y are structurally similar
(isomorphic) objects. Objects are treated as follows by
equal
.
equal
is true of two objects
if they are symbols that are eq
,
if they are numbers that are eql
, or
if they are characters that are eql
.
For conses, equal
is defined recursively as
the two cars being equal
and the two cdrs being equal
.
Two arrays are equal
only if they are eq
,
with one exception:
strings and bit vectors are compared elementbyelement (using eql
).
If either x or y has a fill pointer, the
fill pointer limits
the number of elements examined by equal
.
Uppercase and lowercase letters in strings are considered by
equal
to be different.
Two pathnames are equal
if and only if
all the corresponding components
(host, device, and so on) are
equivalent. Whether or not
uppercase and lowercase letters are considered equivalent
in strings appearing in components is implementationdependent.
pathnames
that are equal
should be functionally equivalent.
Two other objects are equal
only if they are eq
.
equal
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 equal
,
with upper
entries taking priority over lower ones.

Figure 5.12: Summary and priorities of behavior of equal
Any two objects that are eql
are also equal
.
equal
may fail to terminate if x or y is circular.
(equal 'a 'b) → false (equal 'a 'a) → true (equal 3 3) → true (equal 3 3.0) → false (equal 3.0 3.0) → true (equal #c(3 4) #c(3 4)) → true (equal #c(3 4.0) #c(3 4)) → false (equal (cons 'a 'b) (cons 'a 'c)) → false (equal (cons 'a 'b) (cons 'a 'b)) → true (equal #\A #\A) → true (equal #\A #\a) → false (equal "Foo" "Foo") → true (equal "Foo" (copyseq "Foo")) → true (equal "FOO" "foo") → false (equal "Thisstring" "Thisstring") → true (equal "Thisstring" "thisstring") → false
eq, eql (Function), equalp, =, string=, stringequal, char=, charequal, treeequal
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.
A rough rule of thumb is that two objects are equal
if and only if their printed representations are the same.