initial checkin

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

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,
+		)
+	}
+}