New PRINT At Run-Time (Retracted)

After considering this design, it was decided to be more complicated than it needed to be, so this post has been retracted, see revised post.

Consider the previous example statement and its new translation:

PRINT A,B$;TAB(20);C%
A B$ 20 C% PrintDbl , PrintStr TAB( PrintInt PRINT

At run-time, in additional to the evaluation stack used to hold values of operands and results, there will also be a command stack (not to be confused with the current command stack used by the old translator routines, but not needed by the new translator routines).  The special print codes (specific print type codes, comma, and print functions), will only push themselves to the command stack.

When the PRINT (or semicolon) code is executed, it will process the command stack, except it will start at the bottom of the stack instead of popping items from the top.  This is possible because the QStack class is derived from the QVector class, which allows its elements to be access by index.  The values of the evaluation stack will also be accessed the same way.

When the PRINT (or semicolon) begins, it will start with indexes (one for each stack) set to zero and will process each item on the command stack.  For the specific print type code, it will access the value at the evaluation stack index, output it, and increment the index.  For a comma code, it will output the appropriate number of spaces (leaving the evaluation stack index as is).  For a print function (TAB or SPC), it will access the value at the evaluation stack index, output the appropriate number of spaces, and increment the index.

At the end (top) of the command stack, it will clear both stacks, return the indexes to zero (for the next command), and for the PRINT code only, will advance to the next line.  This scheme works because both the evaluation and command stacks will be empty at the beginning of each command.