Add functional nor predicate (#172)

function/predicate.go

@@ -32,3 +32,16 @@ func Or[T any](predicates ...func(T) bool) func(T) bool {
 		return false // False if all predicates are false
 	}
 }
+
+// Nor returns a composed predicate that represents the logical NOR of a list of predicates.
+// It evaluates to true only if all predicates evaluate to false for the given value.
+func Nor[T any](predicates ...func(T) bool) func(T) bool {
+	return func(value T) bool {
+		for _, predicate := range predicates {
+			if predicate(value) {
+				return false // If any predicate evaluates to true, the NOR result is false
+			}
+		}
+		return true // Only returns true if all predicates evaluate to false
+	}
+}

function/predicate_test.go

@@ -54,6 +54,26 @@ func TestPredicatesAndPure(t *testing.T) {
 	assert.ShouldBeFalse(isNumericAndLength5("abcde"))
 }
 
+func TestPredicatesNorPure(t *testing.T) {
+	t.Parallel()
+
+	assert := internal.NewAssert(t, "TestPredicatesNorPure")
+
+	match := Nor(
+		func(s string) bool { return strings.ContainsAny(s, "0123456789") },
+		func(s string) bool { return len(s) == 5 },
+	)
+
+	assert.ShouldBeTrue(match("dbcdckkeee"))
+
+	match = Nor(
+		func(s string) bool { return strings.ContainsAny(s, "0123456789") },
+		func(s string) bool { return len(s) == 5 },
+	)
+
+	assert.ShouldBeFalse(match("0123456789"))
+}
+
 func TestPredicatesMix(t *testing.T) {
 	t.Parallel()
 
@@ -72,4 +92,7 @@ func TestPredicatesMix(t *testing.T) {
 	c := Negate(And(a, b))
 
 	assert.ShouldBeFalse(c("hello!"))
+
+	c = Nor(a, b)
+	assert.ShouldBeFalse(c("hello!"))
 }