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procedure+: list-search-positive list predicate
procedure+: list-search-negative list predicate
Returns the first element in list for which predicate is
(respectively) true or false; returns #f if it doesn't find such
an element. (This means that if predicate is true (false) for
#f, it may be impossible to distinguish a successful result from
an unsuccessful one.) Predicate must be a procedure of one
argument.
These procedures return the first pair of list whose car is
object; the returned pair is always one from which list is
composed. If object does not occur in list, #f
(n.b.: not the empty list) is returned. memq uses eq? to
compare object with the elements of list, while memv
uses eqv? and member uses equal?.(10)
(memq 'a '(a b c)) => (a b c) (memq 'b '(a b c)) => (b c) (memq 'a '(b c d)) => #f (memq (list 'a) '(b (a) c)) => #f (member (list 'a) '(b (a) c)) => ((a) c) (memq 101 '(100 101 102)) => unspecified (memv 101 '(100 101 102)) => (101 102)
procedure+: member-procedure predicate
Returns a procedure similar to memq, except that predicate,
which must be an equivalence predicate, is used instead of eq?.
This could be used to define memv as follows:
(define memv (member-procedure eqv?))
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