Add Compose

func.go

@@ -39,3 +39,30 @@ func Partial5[T1, T2, T3, T4, T5, T6, R any](f func(T1, T2, T3, T4, T5, T6) R, a
 		return f(arg1, t2, t3, t4, t5, t6)
 	}
 }
+
+// Compose returns new function that is the composition of 2 functions passed as arguments
+func Compose[T1, T2, T3 any](f1 func(T1) T2, f2 func(T2) T3) func(T1) T3 {
+	return func(t1 T1) T3 {
+		return f2(f1(t1))
+	}
+}
+
+// Compose2 returns new function that is the composition of 2 functions passed as arguments
+func Compose2[T1, T2, T3 any](f1 func(T1) T2, f2 func(T2) T3) func(T1) T3 {
+	return Compose(f1, f2)
+}
+
+// Compose3 returns new function that is the composition of 3 functions passed as arguments
+func Compose3[T1, T2, T3, T4 any](f1 func(T1) T2, f2 func(T2) T3, f3 func(T3) T4) func(T1) T4 {
+	return Compose(Compose(f1, f2), f3)
+}
+
+// Compose4 returns new function that is the composition of 4 functions passed as arguments
+func Compose4[T1, T2, T3, T4, T5 any](f1 func(T1) T2, f2 func(T2) T3, f3 func(T3) T4, f4 func(T4) T5) func(T1) T5 {
+	return Compose(Compose(Compose(f1, f2), f3), f4)
+}
+
+// Compose5 returns new function that is the composition of 5 functions passed as arguments
+func Compose5[T1, T2, T3, T4, T5, T6 any](f1 func(T1) T2, f2 func(T2) T3, f3 func(T3) T4, f4 func(T4) T5, f5 func(T5) T6) func(T1) T6 {
+	return Compose(Compose(Compose(Compose(f1, f2), f3), f4), f5)
+}

func_test.go

@@ -78,3 +78,52 @@ func TestPartial5(t *testing.T) {
 	is.Equal("26", f(10, 9, -3, 0, 5))
 	is.Equal("21", f(-5, 8, 7, -1, 7))
 }
+
+func TestCompose(t *testing.T) {
+	t.Parallel()
+	is := assert.New(t)
+
+	filterEven := func(ns []int) []int {
+		return Filter(ns, func(x int, i int) bool { return x%2 == 0 })
+	}
+	sum := func(ns []int) int {
+		return ReduceRight(ns, func(sum int, x int, i int) int { return sum + x }, 0)
+	}
+	result := Compose(filterEven, sum)([]int{1, 2, 3, 4, 5})
+	is.Equal("6", strconv.Itoa(result))
+}
+
+func TestCompose2(t *testing.T) {
+	t.Parallel()
+	is := assert.New(t)
+
+	filterEven := func(ns []int) []int {
+		return Filter(ns, func(x int, i int) bool { return x%2 == 0 })
+	}
+	sum := func(ns []int) int {
+		return ReduceRight(ns, func(sum int, x int, i int) int { return sum + x }, 0)
+	}
+	result := Compose2(filterEven, sum)([]int{1, 2, 3, 4, 5})
+	is.Equal("6", strconv.Itoa(result))
+}
+
+func TestCompose3(t *testing.T) {
+	t.Parallel()
+	is := assert.New(t)
+
+	filterEven := func(ns []int) []int {
+		return Filter(ns, func(x int, i int) bool { return x%2 == 0 })
+	}
+	mulEachBy10 := func(ns []int) []int {
+		return Map(ns, func(x int, i int) int { return x * 10 })
+	}
+	sum := func(ns []int) int {
+		return ReduceRight(ns, func(sum int, x int, i int) int { return sum + x }, 0)
+	}
+	result := Compose3(
+		filterEven,
+		mulEachBy10,
+		sum,
+	)([]int{1, 2, 3, 4, 5})
+	is.Equal("60", strconv.Itoa(result))
+}