Implemented expression parsing

src/build/token/Token.go

@@ -12,16 +12,23 @@ type Token struct {
 }
 
 // After returns the position after the token.
-func (t Token) After() int {
+func (t *Token) After() int {
 	return t.Position + len(t.Bytes)
 }
 
 // String creates a human readable representation for debugging purposes.
-func (t Token) String() string {
+func (t *Token) String() string {
 	return fmt.Sprintf("%s %s", t.Kind, t.Text())
 }
 
+// Reset resets the token to default values.
+func (t *Token) Reset() {
+	t.Kind = Invalid
+	t.Position = 0
+	t.Bytes = nil
+}
+
 // Text returns the token text.
-func (t Token) Text() string {
+func (t *Token) Text() string {
 	return string(t.Bytes)
 }