Translator – LET Command (Implementation)

The SimpleStack class is used for the new command stack, which will hold a CmdItem structure consisting of a token pointer and a code. The code will initially be set from the token's index, but may be changed to other associated codes as commands are processed by the Translator. Since the hold and done stacks are also simple stacks, these were changed from the List class to the SimpleStack class. This only required minor changes to push and pop calls for these stacks.

As previously hinted, the Translator status enumeration needed to be moved outside the Translator class before the TableEntry structure. The enumeration was renamed TokenStatus as that seemed appropriate for the return value of the Translator's add token function. Each of the enumeration values were also renamed except for the BUG statuses, which were left alone.

A previously mentioned, the mode must be changed from Command to Assignment upon receiving the LET command token. Some commands will need to change the mode from Command to Expression (PRINT, IF, WHILE, etc.). Some commands will need to change the mode from Command to a new End-of-Statement mode, since nothing is expected after command keyword (END IF, DO, LOOP, etc.).

Having an every growing switch statement of the command code is not efficient. Therefore, a next token mode value was added to the TableEntry structure. When a command token is received, if the mode is currently Command, then the mode will be changed to the command's table entry next token mode value. The command will be pushed onto the command stack along with it's current code. No further action needs to be taken until the rest of the statement is processed.

Since there will be mode values in the TableEntry structure, the Translator mode enumeration was also moved before TableEntry and renamed TokenMode (again an appropriate name). The enumeration values were also renamed to reflect this. For now, if the next token mode is not set for a command (a new Null token mode value), then a “not yet implemented” bug error occurs. If the current mode is not Command, then a new “unexpected command” message occurs.

For the LET command, the next token mode value is Assignment. When an assignment operator is added to the output list, if there is a LET command on the command stack, it is popped and the assignment operator's token's LET sub-code flag is set. For now, since the command stack should be empty, the end-of-line processing only needs to check if the command stack is empty. Later it will need to process commands on the stack.