Translation – Command Token Issues

The last problem statements related to unexpected command tokens were:

A PRINT B
MID$(A$ PRINT,4)=""

The first statement gave an “expected operator or end-of-statement” error at the B token. The second statement was actually accepted, but with a strange translation. The problems were caused because when the PRINT command token was received, it was immediately pushed to the command stack because the mode was still set to command.

Both statements start as assignment statements, but assignment mode was not being set (unless preceded by the LET keyword). When an equal token is received expression mode is set, or when a comma token is received assignment list mode is set. The “unexpected command” error was only occurring when the mode was not set to command, which didn't occur with the statements above. Also, this message again does fit with the “expected ...” type of message.

Once a command token is received in command mode, the mode is set according to the token mode in the command's table entry. A change was made to the process operand routine that once an operand token is processed, if in command mode, the operand is assumed the beginning of an assignment statement and so the mode is changed to assignment.

To remove the “unexpected command” error and report a more appropriate error, the command token has to be passed through the rest of the Translator. This will occur when the Translator is not in command mode. So the main add token routine was changed to not report this error if a command token is received and the mode is not command.

Command tokens received in operand state were already being reported correctly since commands are also considered operators, which are not valid operands (unless the operator is a unary operator, which commands are not). Commands are considered operators because some commands can be found where an operator is expected, for example, THEN and ELSE.

Commands tokens received in operator state are only valid if they have a token handler. In the process operator routine, when an operator token does not have a token handler a default operator token handler is called. Before the default operator token handler is called, a check was added to return an appropriate error if the token is a command.