initial checkin

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

magma/array.go

@@ -0,0 +1,29 @@
+package magma
+
+import (
+	F "github.com/ibm/fp-go/function"
+	AR "github.com/ibm/fp-go/internal/array"
+)
+
+func GenericMonadConcatAll[GA ~[]A, A any](m Magma[A]) func(GA, A) A {
+	return func(as GA, first A) A {
+		return AR.Reduce(as, m.Concat, first)
+	}
+}
+
+// GenericConcatAll concats all items using the semigroup and a starting value
+func GenericConcatAll[GA ~[]A, A any](m Magma[A]) func(A) func(GA) A {
+	ca := GenericMonadConcatAll[GA](m)
+	return func(a A) func(GA) A {
+		return F.Bind2nd(ca, a)
+	}
+}
+
+func MonadConcatAll[A any](m Magma[A]) func([]A, A) A {
+	return GenericMonadConcatAll[[]A](m)
+}
+
+// ConcatAll concats all items using the semigroup and a starting value
+func ConcatAll[A any](m Magma[A]) func(A) func([]A) A {
+	return GenericConcatAll[[]A](m)
+}

magma/magma.go

@@ -0,0 +1,84 @@
+package magma
+
+type Magma[A any] interface {
+	Concat(x A, y A) A
+}
+
+type magma[A any] struct {
+	c func(A, A) A
+}
+
+func (self magma[A]) Concat(x A, y A) A {
+	return self.c(x, y)
+}
+
+func MakeMagma[A any](c func(A, A) A) Magma[A] {
+	return magma[A]{c: c}
+}
+
+func Reverse[A any](m Magma[A]) Magma[A] {
+	return MakeMagma(func(x A, y A) A {
+		return m.Concat(y, y)
+	})
+}
+
+func filterFirst[A any](p func(A) bool, c func(A, A) A, x A, y A) A {
+	if p(x) {
+		return c(x, y)
+	}
+	return y
+}
+
+func filterSecond[A any](p func(A) bool, c func(A, A) A, x A, y A) A {
+	if p(y) {
+		return c(x, y)
+	}
+	return x
+}
+
+func FilterFirst[A any](p func(A) bool) func(Magma[A]) Magma[A] {
+	return func(m Magma[A]) Magma[A] {
+		c := m.Concat
+		return MakeMagma(func(x A, y A) A {
+			return filterFirst(p, c, x, y)
+		})
+	}
+}
+
+func FilterSecond[A any](p func(A) bool) func(Magma[A]) Magma[A] {
+	return func(m Magma[A]) Magma[A] {
+		c := m.Concat
+		return MakeMagma(func(x A, y A) A {
+			return filterSecond(p, c, x, y)
+		})
+	}
+}
+
+func first[A any](x A, y A) A {
+	return x
+}
+
+func second[A any](x A, y A) A {
+	return y
+}
+
+func First[A any]() Magma[A] {
+	return MakeMagma(first[A])
+}
+
+func Second[A any]() Magma[A] {
+	return MakeMagma(second[A])
+}
+
+func endo[A any](f func(A) A, c func(A, A) A, x A, y A) A {
+	return c(f(x), f(y))
+}
+
+func Endo[A any](f func(A) A) func(Magma[A]) Magma[A] {
+	return func(m Magma[A]) Magma[A] {
+		c := m.Concat
+		return MakeMagma(func(x A, y A) A {
+			return endo(f, c, x, y)
+		})
+	}
+}

magma/magma_test.go

@@ -0,0 +1,19 @@
+package magma
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFirst(t *testing.T) {
+	m := First[string]()
+
+	assert.Equal(t, "a", m.Concat("a", "b"))
+}
+
+func TestSecond(t *testing.T) {
+	m := Second[string]()
+
+	assert.Equal(t, "b", m.Concat("a", "b"))
+}