type Cons[a any] struct {
	Head a
	Tail List[a]
}

func (xs Cons[a]) Match(casenil Function[Nil[a], any], casecons Function[Cons[a], any]) any {
	return casecons.Apply(xs)
}

type mapNil[a, b any] struct {
}

func (m mapNil[a, b]) Apply(_ Nil[a]) any {
	return Nil[b]{}
}

type mapCons[a, b any] struct {
	f Function[a, b]
}

func (m mapCons[a, b]) Apply(xs Cons[a]) any {

	}
	return n, nil
}

// A mapDir is a directory fs.File (so also an fs.ReadDirFile) open for reading.
type mapDir struct {
	path string
	mapFileInfo
	entry  []mapFileInfo
	offset int
}

func (d *mapDir) Stat() (fs.FileInfo, error) { return &d.mapFileInfo, nil }
func (d *mapDir) Close() error               { return nil }
func (d *mapDir) Read(b []byte) (int, error) {

	}
	if err := TestFS(m, "hello", "fortune", "fortune/k", "fortune/k/ken.txt"); err != nil {
		t.Fatal(err)
	}
}

func TestMapFSChmodDot(t *testing.T) {
	m := MapFS{
		"a/b.txt": &MapFile{Mode: 0666},
		".":       &MapFile{Mode: 0777 | fs.ModeDir},
	}
	buf := new(strings.Builder)
	fs.WalkDir(m, ".", func(path string, d fs.DirEntry, err error) error {
		fi, err := d.Info()
		if err != nil {
			return err
		}

	nestedVal.AddField(flags)
	nestedVal.AddField(dates)
	nested := apiservercel.NewField(3, "nested")
	nested.Ref = testValue(t, 4, nestedVal)
	mapVal := apiservercel.NewMapValue()
	mapVal.AddField(name)
	mapVal.AddField(nested)
	//rule := rt.ConvertToRule(testValue(t, 11, mapVal))
	//if rule == nil {
	//	t.Error("map could not be converted to rule")
	//}
	//if rule.GetID() != 11 {

		{"sliceLit[1]", sliceLit[1], 25},
		{"sliceLit[2]", sliceLit[2], 25},
		{"sliceLit[3]", sliceLit[3], 26},

		{"mapLit[29]", mapLit[29], 29},
		{"mapLit[30]", mapLit[30], 30},
		{"mapLit[31]", mapLit[31+firstLine] + firstLine, 31}, // nb it's the key not the value
		{"mapLit[32]", mapLit[32+firstLine] + firstLine, 32}, // nb it's the key not the value

		{"intLit", intLit - 2*firstLine, 34 + 35 + 36},

		if path[0] == "" {
			return nil, false, fmt.Errorf("getFromStructPath path %s, empty map key value", path)
		}
		mapVal := val.MapIndex(reflect.ValueOf(path[0]))
		if !mapVal.IsValid() {
			return nil, false, fmt.Errorf("getFromStructPath path %s, path does not exist", path)
		}
		return getFromStructPath(mapVal.Interface(), path[1:])
	case reflect.Slice:
		idx, err := strconv.Atoi(path[0])
		if err != nil {

#                                                      Mail
#                                                     ------
# Does it send mock mail? (true: no send actually, logging only)
mail.send.mock = true

# SMTP server settings for main: host:port
mail.smtp.server.main.host.and.port = localhost:25

# The prefix of subject to show test environment or not
mail.subject.test.prefix = [Test]

# The common return path of all mail

#                                                      Mail
#                                                     ------
# Does it send mock mail? (true: no send actually, logging only)
mail.send.mock = false

# SMTP server settings for main: host:port
mail.smtp.server.main.host.and.port = localhost:25

# The prefix of subject to show test environment or not
mail.subject.test.prefix = 

# The common return path of all mail

#                                                      Mail
#                                                     ------
# Does it send mock mail? (true: no send actually, logging only)
mail.send.mock = false

# SMTP server settings for main: host:port
mail.smtp.server.main.host.and.port = localhost:25

# The prefix of subject to show test environment or not
mail.subject.test.prefix = 

# The common return path of all mail

#                                                      Mail
#                                                     ------
# Does it send mock mail? (true: no send actually, logging only)
mail.send.mock = false

# SMTP server settings for main: host:port
mail.smtp.server.main.host.and.port = localhost:25

# The prefix of subject to show test environment or not
mail.subject.test.prefix = 

# The common return path of all mail