The ORD_KEY signature defines an interface to an abstract type
of keys with a comparison function. This signature is used as
the argument to various implementations of finite maps and sets.
Synopsis
signature ORD_KEYInterface
type ord_key
val compare : ord_key * ord_key -> orderDescription
type ord_key-
The abstract key type.
val compare : ord_key * ord_key -> order-
compare (k1, k2)returns the relation between the two keys. This function should define a total order on theord_keytype.