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Go to the previous, next section. Searching Lists 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. procedure: memq object list procedure: memv object list procedure: member object list 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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