Recreator – Design Considerations

Originally, there was going to be another module, the decoder, which would convert internal program code into an RPN (Reverse Polish Notation) token list (like the translator produces).  The recreator would then convert the RPN list back into the program text (close to the originally entered code).  Very early on (see December 19, 2009) this step was considered simple and unnecessary and so was combined into the recreator.

The program model needs to detect when a changed line has actually been changed.  The edit box sometimes reports changes lines when the line has not actually change.  The user could also have simply added spaces to the line (which are not stored) or changed the case of a keyword, which would not result in a change to the internal program code.  As previously mentioned, comparing the internal code of the current line with to the new line is problematic.

The new line would first have to be encoded, which will affect the dictionaries.  Either this would need to be undone, or the old line removed first to dereference dictionary entries only to have them referenced again when putting in the new line.  This is acceptable for simple dictionaries (variables, constants, remarks, etc.), but is much more involved with the blocking commands (IF-END IF, FOR-NEXT, etc.), where the block will probably be kept in a block dictionary.

A better alternative is to convert the program line into an intermediate RPN token list (decoded).  The translated RPN list of the new line and be compared to the decoded RPN list of the current line.  Since the decode operation can be contained in a single routine like the encode operation, the program model will own this decode routine also.

Since the decode routine will be present, then it makes sense for the recreator to take a decoded RPN list as input to convert to the program text.  This method has another advantage for testing.  Currently, the test code translates expressions and statements into RPN lists.  These RPN lists can then be passed to the recreator for testing, therefore there will be a new test mode for taking these existing tests, translate them to RPN lists, and then recreate them back to text.