add null data type

README.md

@@ -43,6 +43,12 @@ A boolean value is either `true` or `false` of any case.
 
 `TRUE`, `true`, `True`, `FALSE`, `False`, `false`.
 
+### Null
+
+A null value is allowed as `null` of any case.
+
+`NULL`, `Null`, `null`.
+
 ### String
 A string value is wrapped by double quotes (single quotes will not work).
 

config/config.go

@@ -8,6 +8,7 @@ const (
 	BOOLEAN
 	FLOAT
 	STRING
+	NULL
 )
 
 var configTypes = [...]string{
@@ -16,6 +17,7 @@ var configTypes = [...]string{
 	INTEGER: "INTEGER",
 	FLOAT:   "FLOAT",
 	STRING:  "STRING",
+	NULL:    "NULL",
 }
 
 func (this ConfigType) String() string {
@@ -44,6 +46,14 @@ type BooleanValue struct {
 func (this BooleanValue) GetType() ConfigType   { return BOOLEAN }
 func (this BooleanValue) GetValue() interface{} { return this.Value }
 
+type NullValue struct {
+	Name  string
+	Value interface{}
+}
+
+func (this NullValue) GetType() ConfigType   { return NULL }
+func (this NullValue) GetValue() interface{} { return nil }
+
 type IntegerValue struct {
 	Name  string
 	Value int64

example/example.cfg

@@ -5,6 +5,7 @@ master {
   float = 80.80;
   boolean = true;
   negative = FALSE;
+  nothing = NULL;
   sub {
       key = "master sub key value";
   }

parser/parser.go

@@ -128,6 +128,11 @@ func (this *Parser) parseSetting(name string) error {
 			Name:  name,
 			Value: bool_val,
 		}
+	case token.NULL:
+		value = config.NullValue{
+			Name:  name,
+			Value: nil,
+		}
 	case token.INTEGER:
 		int_val, err := strconv.ParseInt(this.cur_tok.Literal, 10, 64)
 		if err != nil {

token/tokenid.go

@@ -17,6 +17,7 @@ const (
 	INTEGER
 	FLOAT
 	STRING
+	NULL
 )
 
 var tokenNames = [...]string{
@@ -32,6 +33,7 @@ var tokenNames = [...]string{
 	INTEGER:    "INTEGER",
 	FLOAT:      "FLOAT",
 	STRING:     "STRING",
+	NULL:       "NULL",
 }
 
 func (this TokenID) String() string {

token/tokenizer.go

@@ -25,6 +25,10 @@ func isBoolean(str string) bool {
 	return lower == "true" || lower == "false"
 }
 
+func isNull(str string) bool {
+	return strings.ToLower(str) == "null"
+}
+
 type Tokenizer struct {
 	cur_line int
 	cur_col  int
@@ -80,6 +84,8 @@ func (this *Tokenizer) parseIdentifier() {
 
 	if isBoolean(this.cur_tok.Literal) {
 		this.cur_tok.ID = BOOLEAN
+	} else if isNull(this.cur_tok.Literal) {
+		this.cur_tok.ID = NULL
 	}
 }