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After considering this design, it was decided to be more complicated than it needed to be, so this post has been retracted, see revised post.

The run-time design of the PRINT statement was reconsidered.  The old scheme inserted specific type print codes into the translation with an optional PRINT code at the end depending if the line ended with a semicolon, comma or print function (TAB or SPC).  Consider this example statement and its old translation:

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

The specific type print codes pop a value from the evaluation stack and outputs it.  The comma token outputs spaces to advance the cursor to the next column (traditionally groups of 8 characters).  The TAB print function outputs spaces to advance to specified column.  And the final PRINT advances to the next line.  If the line ended with a semicolon, comma or print function, the final PRINT code is not present.  The new translation will look like this (details to follow):

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

The final PRINT code is always present, and at run time will know when to advance to the next line (depends on the code immediately preceding it).  Semicolon tokens (or a sub-code) is not necessary and is implied between the items to print.  Multiple semicolons, though allowed in the old translator (the semicolon sub-code and any semicolon tokens would do nothing at run-time), will not be permitted as there is no reason to allow them (unlike multiple commas).

A semicolon at the end of the line needs special consideration.  If there is a semicolon at the end of the line, it will take the place of the PRINT code.  At run-time, both perform the same actions except only PRINT advances to the next line.  A semicolon can be used this way since no other statement needs a semicolon token.  A 'Keep' sub-code or a new PrintKeep code could have been used, but why have a sub-code check at run-time or create a new code when a semicolon token can be used.

The next post will contain the details of how this new PRINT translation will work at run-time...