new operator ':=', it assigns a value to a variable by deep copy

scan/scanner.go

@@ -192,6 +192,8 @@ func (scanner *Scanner) fetchNextToken() (tk *Token) {
 		case ':':
 			if next, _ := scanner.peek(); next == ':' {
 				tk = scanner.moveOn(SymDoubleColon, ch, next)
+			} else if next == '=' {
+				tk = scanner.moveOn(SymColonEqual, ch, next)
 			} else {
 				tk = scanner.MakeToken(SymColon, ch)
 			}