2 files changed, 117 insertions, 0 deletions
diff --git a/src/gobang.go b/src/gobang.go
index 2985d19..1826a5f 100644
--- a/src/gobang.go
+++ b/src/gobang.go
@@ -65,6 +65,30 @@ var (
 
 
 
+func MapIndexed[A any, B any](fn func(A, int) B, coll []A) []B {
+	out := make([]B, len(coll))
+	for i, x := range coll {
+		out[i] = fn(x, i)
+	}
+	return out
+}
+
+func Map[A any, B any](fn func(A) B, coll []A) []B {
+	return MapIndexed(func(x A, _ int) B {
+		return fn(x)
+	}, coll)
+}
+
+func Filter[A any](fn func(A) bool, coll []A) []A {
+	out := []A{}
+	for _, x := range coll {
+		if fn(x) {
+			out = append(out, x)
+		}
+	}
+	return out
+}
+
 func PanicIf(err error) {
 	if err != nil {
 		panic(err)
diff --git a/tests/gobang.go b/tests/gobang.go
index 32f6d99..56e3978 100644
--- a/tests/gobang.go
+++ b/tests/gobang.go
@@ -15,6 +15,96 @@ import (
 
 
 
+func test_MapIndexed() {
+	TestStart("MapIndexed()")
+
+	Testing("empty array", func() {
+		noop := func(s string, i int) string {
+			return s
+		}
+
+		arr := []string{}
+		TAssertEqual(MapIndexed(noop, arr), arr)
+	})
+
+	Testing("replace content with index", func() {
+		index := func(s string, i int) int {
+			return i
+		}
+
+		TAssertEqual(
+			MapIndexed(index, []string{"a", "b", "c"}),
+			[]int{0, 1, 2},
+		)
+	})
+
+	Testing("a computed value", func() {
+		fn := func(x int, i int) int {
+			return x + i
+		}
+
+		TAssertEqual(
+			MapIndexed(fn, []int{1, 2, 3, 4, 5}),
+			[]int{1, 3, 5, 7, 9},
+		)
+	})
+}
+
+func test_Map() {
+	TestStart("Map()")
+
+	Testing("empty array", func() {
+		noop := func(s string) string {
+			return s
+		}
+
+		arr := []string{}
+		TAssertEqual(Map(noop, arr), arr)
+	})
+
+	Testing("a derived value", func() {
+		appendBang := func(s string) string {
+			return s + "!"
+		}
+
+		TAssertEqual(
+			Map(appendBang, []string{"a", "b", "c"}),
+			[]string{"a!", "b!", "c!"},
+		)
+	})
+}
+
+func test_Filter() {
+	TestStart("Filter()")
+
+	fn := func(i int) bool {
+		return i < 10
+	}
+
+
+	Testing("empty array", func() {
+		arr := []int{}
+		TAssertEqual(Filter(fn, arr), arr)
+	})
+
+	Testing("filters everything", func() {
+		arr := []int{10, 11, 12, 13, 14, 15}
+		TAssertEqual(Filter(fn, arr), []int{})
+	})
+
+	Testing("filters nothing", func() {
+		arr := []int{1, 2, 3, 4, 5}
+		TAssertEqual(Filter(fn, arr), arr)
+	})
+
+	Testing("filters some", func() {
+		TAssertEqual(
+			Filter(fn, []int{8, 9, 10, 11, 12, 0, 13}),
+			[]int{8, 9, 0},
+		)
+	})
+}
+
 func test_PanicIf() {
 	TestStart("PanicIf()")
 
@@ -1354,6 +1444,9 @@ func test_setHostname() {
 func MainTest() {
 	Init()
 
+	test_MapIndexed()
+	test_Map()
+	test_Filter()
 	test_PanicIf()
 	test_Must()
 	test_Clamp()