member

member takes any value and a list, and searches the list for that value. If it finds it, it returns a pointer to the first pair whose car holds that value, i.e., the "rest" of the list starting at the point where the searched-for item was found. If it is not found, #f is returned. (The return value is therefore always either a pair or the false object.)

(member 22 '(18 22 #f 300))

returns (22 #f 300).

Notice that member can be used either to find a value's location in a list, or as a predicate to check whether the item is in the list at all. Since pairs are true values, you can use the result of member in a conditional expression and it will count as true if the item is found.

[ Maybe I should introduce strings and symbols here, moving some material from the tutorial chapter here and possibly expanding the tutorial with more examples. ]