fix: add support for context sensitive readers

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

internal/readert/reader.go

@@ -0,0 +1,44 @@
+package readert
+
+import (
+	F "github.com/ibm/fp-go/function"
+	R "github.com/ibm/fp-go/reader/generic"
+)
+
+// here we implement the monadic operations using callbacks from
+// higher kinded types, as good a golang allows use to do this
+
+func MonadMap[GEA ~func(E) HKTA, GEB ~func(E) HKTB, E, A, B, HKTA, HKTB any](fmap func(HKTA, func(A) B) HKTB, fa GEA, f func(A) B) GEB {
+	return R.MonadMap[GEA, GEB](fa, F.Bind2nd(fmap, f))
+}
+
+func MonadChain[GEA ~func(E) HKTA, GEB ~func(E) HKTB, A, E, HKTA, HKTB any](fchain func(HKTA, func(A) HKTB) HKTB, ma GEA, f func(A) GEB) GEB {
+	return R.MakeReader(func(r E) HKTB {
+		return fchain(ma(r), func(a A) HKTB {
+			return f(a)(r)
+		})
+	})
+}
+
+func MonadOf[GEA ~func(E) HKTA, E, A, HKTA any](fof func(A) HKTA, a A) GEA {
+	return R.MakeReader(func(_ E) HKTA {
+		return fof(a)
+	})
+}
+
+// HKTFAB = HKT[func(A)B]
+func MonadAp[GEA ~func(E) HKTA, GEB ~func(E) HKTB, GEFAB ~func(E) HKTFAB, E, A, HKTA, HKTB, HKTFAB any](fap func(HKTFAB, HKTA) HKTB, fab GEFAB, fa GEA) GEB {
+	return R.MakeReader(func(r E) HKTB {
+		return fap(fab(r), fa(r))
+	})
+}
+
+func MonadFromReader[GA ~func(E) A, GEA ~func(E) HKTA, E, A, HKTA any](
+	fof func(A) HKTA, ma GA) GEA {
+	return R.MakeReader(F.Flow2(ma, fof))
+}
+
+func FromReader[GA ~func(E) A, GEA ~func(E) HKTA, E, A, HKTA any](
+	fof func(A) HKTA) func(ma GA) GEA {
+	return F.Bind1st(MonadFromReader[GA, GEA, E, A, HKTA], fof)
+}