Major Section: ACL2-BUILT-INS
General Forms: (remove-duplicates x) (remove-duplicates x :test 'eql) ; same as above (eql as equality test) (remove-duplicates x :test 'eq) ; same, but eq is equality test (remove-duplicates x :test 'equal) ; same, but equal is equality test
(Remove-duplicates x) returns the result of deleting duplicate elements
from the beginning of the list or string x. For example,
(remove-duplicates '(1 2 3 2 4)) is equal to '(1 3 2 4). The
optional keyword, :TEST, has no effect logically, but provides the
test (default eql) used for comparing x with successive elements of
lst.
The guard for a call of remove-duplicates depends on the test. In
all cases, the argument must satisfy stringp or true-listp. If
the test is eql, then the argument must satisfy either stringp or
eqlable-listp. If the test is eq, then the argument must satisfy
symbol-listp.
The relation between remove-duplicates and its variants is related to the
usual pattern for equality variants; see equality-variants. However, the
possibility of a string argument changes the usual pattern a bit. As one
might expect:
(remove-duplicates-eq lst)is equivalent to(remove-duplicates lst :test 'eq).
However, remove-duplicates-equal is defined without consideration of
strings, for backward compatibility with versions of ACL2 through
Version_4.2. The macro remove-duplicates-logic has been introduced to
model the behavior of remove-duplicates even on strings; use
:pe if you wish to see its definition. So we can say the
following.
(remove-duplicates-logic lst)is equivalent to(remove-duplicates lst :test 'equal); and
(remove-duplicates-logic lst)is equal to(remove-duplicates-equal lst)whenlstis not a string.
In particular, when the argument is not a string, reasoning about any of
these primitives reduces to reasoning about the function
remove-duplicates-equal.
Remove-duplicates is defined by Common Lisp. See any Common Lisp
documentation for more information.