Question

Just out of curiosity: if I have a class operator (or function or the like) that accepts several arguments (normally 1 or 2) and returns 1 of 3 values (instead of boolean true or false) should it still be called a predicate? Or a special case of fuzzy logic? Or what?

Example:
template <class T>
class BinaryPredicate {
public:
virtual int operator()(const T& lhs, const T& rhs) const = 0;
};

which returns -1, 0 or 1 according to a defined inherited operator function (for example to determine order).

Answer 1

Hm, you are returning concrete values from your function, and there is nothing fuzzy in them, you are more in three-valued logic domain (sometimes called trivalent) than in fuzzy domain. For example, trivalent is very popular in electronic(three state logic). Device can be in 3 states: Logical one (true), logical zero(false) and high impedance.