new prefix operator "!" as logic NOT

parser.go

@@ -444,8 +444,7 @@ func (parser *parser) parseGeneral(scanner *scanner, ctx parserContext, termSymb
 			} else if tk.IsSymbol(SymStar) {
 				tk.SetSymbol(SymDereference)
 			} else if tk.IsSymbol(SymExclamation) {
-				err = tk.Errorf("postfix opertor %q requires an operand on its left side", tk)
-				break
+				tk.SetSymbol(SymNot)
 			}
 			firstToken = false
 		}