feat(higherorder): adding generic Filter function (#141)

* feat(higherorder): adding generic Filter function
* fix(higherorder): with re-factored test for Filter

exp/higherorder/higherorder.go

@@ -26,3 +26,14 @@ func Map[A, B any](f func(A) B, list []A) []B {
 	}
 	return res
 }
+
+// Filter applies a function to each element of a list, if the function returns false those elements are removed, returning a new list
+func Filter[A any](f func(A) bool, list []A) []A {
+	res := make([]A, 0)
+	for _, v := range list {
+		if f(v) {
+			res = append(res, v)
+		}
+	}
+	return res
+}

exp/higherorder/higherorder_test.go

@@ -1,6 +1,10 @@
 package higherorder
 
-import "testing"
+import (
+	"reflect"
+	"strings"
+	"testing"
+)
 
 func Test_Foldl(t *testing.T) {
 	x := Foldl(func(a, b int) int {
@@ -54,3 +58,29 @@ func Test_Map(t *testing.T) {
 		}
 	}
 }
+
+func Test_Filter(t *testing.T) {
+	t.Run("with string slices", func(t *testing.T) {
+		got := Filter(func(a string) bool {
+			return strings.HasPrefix(a, "t")
+		}, []string{"one", "two", "three"})
+
+		want := []string{"two", "three"}
+
+		if !reflect.DeepEqual(got, want) {
+			t.Errorf("Expected %v, got %v", want, got)
+		}
+	})
+
+	t.Run("with int slices", func(t *testing.T) {
+		got := Filter(func(a int) bool {
+			return a%2 == 0
+		}, []int{1, 2, 3, 4, 5})
+
+		want := []int{2, 4}
+
+		if !reflect.DeepEqual(got, want) {
+			t.Errorf("Expected %v, got %v", want, got)
+		}
+	})
+}