initial checkin

Signed-off-by: Dr. Carsten Leue <carsten.leue@de.ibm.com>

predicate/bool.go

@@ -0,0 +1,25 @@
+package predicate
+
+func Not[A any](predicate func(A) bool) func(A) bool {
+	return func(a A) bool {
+		return !predicate((a))
+	}
+}
+
+// And creates a predicate that combines other predicates via &&
+func And[A any](second func(A) bool) func(func(A) bool) func(A) bool {
+	return func(first func(A) bool) func(A) bool {
+		return func(a A) bool {
+			return first(a) && second(a)
+		}
+	}
+}
+
+// Or creates a predicate that combines other predicates via ||
+func Or[A any](second func(A) bool) func(func(A) bool) func(A) bool {
+	return func(first func(A) bool) func(A) bool {
+		return func(a A) bool {
+			return first(a) || second(a)
+		}
+	}
+}

predicate/contramap.go

@@ -0,0 +1,15 @@
+package predicate
+
+import (
+	F "github.com/ibm/fp-go/function"
+)
+
+// ContraMap creates a predicate from an existing predicate given a mapping function
+func ContraMap[A, B any](f func(B) A) func(func(A) bool) func(B) bool {
+	return func(pred func(A) bool) func(B) bool {
+		return F.Flow2(
+			f,
+			pred,
+		)
+	}
+}

predicate/monoid.go

@@ -0,0 +1,43 @@
+package predicate
+
+import (
+	F "github.com/ibm/fp-go/function"
+	M "github.com/ibm/fp-go/monoid"
+	S "github.com/ibm/fp-go/semigroup"
+)
+
+// SemigroupAny combines predicates via ||
+func SemigroupAny[A any](predicate func(A) bool) S.Semigroup[func(A) bool] {
+	return S.MakeSemigroup(func(first func(A) bool, second func(A) bool) func(A) bool {
+		return F.Pipe1(
+			first,
+			Or(second),
+		)
+	})
+}
+
+// SemigroupAll combines predicates via &&
+func SemigroupAll[A any](predicate func(A) bool) S.Semigroup[func(A) bool] {
+	return S.MakeSemigroup(func(first func(A) bool, second func(A) bool) func(A) bool {
+		return F.Pipe1(
+			first,
+			And(second),
+		)
+	})
+}
+
+// MonoidAny combines predicates via ||
+func MonoidAny[A any](predicate func(A) bool) S.Semigroup[func(A) bool] {
+	return M.MakeMonoid(
+		SemigroupAny(predicate).Concat,
+		F.Constant1[A](false),
+	)
+}
+
+// MonoidAll combines predicates via &&
+func MonoidAll[A any](predicate func(A) bool) S.Semigroup[func(A) bool] {
+	return M.MakeMonoid(
+		SemigroupAll(predicate).Concat,
+		F.Constant1[A](true),
+	)
+}