Translator – Token/Command Handler Restructuring

While looking over the design notes for the INPUT and INPUT PROMPT commands, besides implementing a new INPUT command handler, parts would also be implemented in the Comma and Semicolon token handlers just like the PRINT command. As further commands are implemented, these token handlers will increase in size. The code to handle a command will be located in several different routines. A better design would be if all of the command is processed in a single routine – the command handler.

The EOL token handler already calls the command handler, where each currently assumes that it is called for an EOL token. The code that would be in the comma and semicolon token handlers could be moved to the command handler, which would have a switch on the code of the token passed in to perform the appropriate action. Then the comma and semicolon token handlers would also call a command handler. If the command doesn't support the passed token, then it would return an error.

There is a sequence of code to call a command handler: get the command item from on top of the command stack, get the command token's command handler from the table, return an error if there is no handler in the table, call the command handler, if it returns an error then check if the command handler changed the token (for the error) and if is has delete the original token passed, and set the error token to return. This sequence will be put into a new call command handler routine so the code is not repeated in each token handler.