predicate.go

package fuego

// Predicate represents a predicate (boolean-valued function) of one argument.
// Could also be: `type Predicate[T any] Function[T, bool]`.
type Predicate[T any] func(t T) bool

// And is a composed predicate that represents a short-circuiting logical
// AND of this predicate and another.
func (p Predicate[T]) And(other Predicate[T]) Predicate[T] {
	return func(t T) bool {
		if p == nil || other == nil {
			return False[T]()(t)
		}

		return p(t) && other(t)
	}
}

// Or is a composed predicate that represents a short-circuiting logical
// OR of two predicates.
func (p Predicate[T]) Or(other Predicate[T]) Predicate[T] {
	return func(t T) bool {
		if p == nil {
			p = False[T]()
		}

		if other == nil {
			return p(t)
		}

		return p(t) || other(t)
	}
}

// Xor is a composed predicate that represents a short-circuiting logical
// XOR of two predicates.
func (p Predicate[T]) Xor(other Predicate[T]) Predicate[T] {
	return func(t T) bool {
		return p.Or(other).And(p.And(other).Negate())(t)
	}
}

// Negate is an alias for Not().
func (p Predicate[T]) Negate() Predicate[T] {
	return p.Not()
}

// Not is the logical negation of a predicate.
func (p Predicate[T]) Not() Predicate[T] {
	return func(t T) bool {
		return p == nil || !p(t)
	}
}

// False returns a predicate that returns always false.
func False[T any]() Predicate[T] {
	return func(T) bool { return false }
}

// True returns a predicate that returns always true.
func True[T any]() Predicate[T] {
	return False[T]().Negate()
}