initial checkin

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

internal/array/traverse.go

@@ -0,0 +1,70 @@
+package array
+
+import (
+	F "github.com/ibm/fp-go/function"
+)
+
+/*
+*
+We need to pass the members of the applicative explicitly, because golang does neither support higher kinded types nor template methods on structs or interfaces
+
+HKTRB = HKT<GB>
+HKTB = HKT<B>
+HKTAB = HKT<func(A)B>
+*/
+func MonadTraverse[GA ~[]A, GB ~[]B, A, B, HKTB, HKTAB, HKTRB any](
+	_of func(GB) HKTRB,
+	_map func(HKTRB, func(GB) func(B) GB) HKTAB,
+	_ap func(HKTAB, HKTB) HKTRB,
+
+	ta GA,
+	f func(A) HKTB) HKTRB {
+	return MonadTraverseReduce(_of, _map, _ap, ta, f, Append[GB, B], Empty[GB]())
+}
+
+func Traverse[GA ~[]A, GB ~[]B, A, B, HKTB, HKTAB, HKTRB any](
+	_of func(GB) HKTRB,
+	_map func(HKTRB, func(GB) func(B) GB) HKTAB,
+	_ap func(HKTAB, HKTB) HKTRB,
+
+	f func(A) HKTB) func(GA) HKTRB {
+
+	return func(ma GA) HKTRB {
+		return MonadTraverse(_of, _map, _ap, ma, f)
+	}
+}
+
+func MonadTraverseReduce[GA ~[]A, GB, A, B, HKTB, HKTAB, HKTRB any](
+	_of func(GB) HKTRB,
+	_map func(HKTRB, func(GB) func(B) GB) HKTAB,
+	_ap func(HKTAB, HKTB) HKTRB,
+
+	ta GA,
+
+	transform func(A) HKTB,
+	reduce func(GB, B) GB,
+	initial GB,
+) HKTRB {
+	mmap := F.Bind2nd(_map, F.Curry2(reduce))
+
+	return Reduce(ta, func(r HKTRB, a A) HKTRB {
+		return _ap(
+			mmap(r),
+			transform(a),
+		)
+	}, _of(initial))
+}
+
+func TraverseReduce[GA ~[]A, GB, A, B, HKTB, HKTAB, HKTRB any](
+	_of func(GB) HKTRB,
+	_map func(HKTRB, func(GB) func(B) GB) HKTAB,
+	_ap func(HKTAB, HKTB) HKTRB,
+
+	transform func(A) HKTB,
+	reduce func(GB, B) GB,
+	initial GB,
+) func(GA) HKTRB {
+	return func(ta GA) HKTRB {
+		return MonadTraverseReduce(_of, _map, _ap, ta, transform, reduce, initial)
+	}
+}