Translator – Print-Only Functions

There are currently two print-only functions, SPC and TAB. Both functions may only be used in a PRINT statement and are not valid in any other expression. There needs to be a new table entry Print flag that will be used for these print-only functions, which are defined as internal functions.

When internal functions are processed (arguments checked and necessary hidden conversion codes inserted), a check is needed that if a function has the Print flag, then the current command on top of the command stack must be a PRINT command otherwise an “invalid use of print function” error occurs. In additional, print-only functions do not have return values, so no result value is pushed onto the done stack. These print-only functions also need to set the flag in the PRINT command item on top of the command stack in case these are the last item in the PRINT statement (to prevent the PRINT code from being appended to the output, which will keep the cursor on the same line at run-time).

During execution at run-time, these functions perform their action directly to the output, which is the reason no result needs to be pushed back on the evaluation stack (the result is outputted instead).

Bug Fix:Upon making the changes for print-only functions, I realized there was an unrelated bug where a command would be accepted after receiving an operand (for example: A LET ...) because the mode was still set to Command. Therefore, when an operand token is processed, if the mode is Command then the mode is set to Assignment – this will prevent a command token from being accepted after an operand.