- (compare-by=/> eq-pred gt-pred [ x y ])procedure
If optional arguments x and y are present then these are compared with respect to the total order defined by the predicate(s) given; the result is in { - 1,0,1}. If x and y are not present then a procedure comparing its two arguments using the predicate(s) given is constructed and returned.
The predicate procedures mean the following: (lt-pred x y) tests if x < y, le-pred tests for <, gt-pred for >, ge-pred for >, and eq-pred tests if x and y are equivalent. The result returned by a predicate procedure is interpreted as a Scheme truth value (i.e. #f is false and non-#f is true).
The purpose of the procedures compare-bypredicate(s) is to define a compare procedure from an order predicate, and possibly an additional equivalence predicate. If an equivalence predicate eq-pred is given, it is called before the order predicate because the equivalence may be coarser than the total ordering, and it may also be cheaper.