initial checkin

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

internal/array/array.go

@@ -0,0 +1,61 @@
+package array
+
+func Slice[GA ~[]A, A any](low, high int) func(as GA) GA {
+	return func(as GA) GA {
+		return as[low:high]
+	}
+}
+
+func IsEmpty[GA ~[]A, A any](as GA) bool {
+	return len(as) == 0
+}
+
+func IsNil[GA ~[]A, A any](as GA) bool {
+	return as == nil
+}
+
+func IsNonNil[GA ~[]A, A any](as GA) bool {
+	return as != nil
+}
+
+func Reduce[GA ~[]A, A, B any](fa GA, f func(B, A) B, initial B) B {
+	current := initial
+	count := len(fa)
+	for i := 0; i < count; i++ {
+		current = f(current, fa[i])
+	}
+	return current
+}
+
+func Append[GA ~[]A, A any](as GA, a A) GA {
+	return append(as, a)
+}
+
+func Empty[GA ~[]A, A any]() GA {
+	return make(GA, 0)
+}
+
+func upsertAt[GA ~[]A, A any](fa GA, a A) GA {
+	buf := make(GA, len(fa)+1)
+	buf[copy(buf, fa)] = a
+	return buf
+}
+
+func UpsertAt[GA ~[]A, A any](a A) func(GA) GA {
+	return func(ma GA) GA {
+		return upsertAt(ma, a)
+	}
+}
+
+func MonadMap[GA ~[]A, GB ~[]B, A, B any](as GA, f func(a A) B) GB {
+	count := len(as)
+	bs := make(GB, count)
+	for i := count - 1; i >= 0; i-- {
+		bs[i] = f(as[i])
+	}
+	return bs
+}
+
+func ConstNil[GA ~[]A, A any]() GA {
+	return (GA)(nil)
+}

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)
+	}
+}