Translator – Single Vs. Multiple Assignments

Some issues came up during the implementation of the assignment handling. A new Assign code is needed for assignment operator. The original plan was that this operator would handle both single and multiple assignments. At run-time, it would simply keeping popping references off of the evaluation stack and assign the value until the stack is empty. However, this requires a check if the stack is empty. The goal is to reduce the number of checks that is needed at run-time because the more checks made, the more time wasted doing these checks during program execution.

Since a single assignment will be the common case and multiple assignment the exception, the single assignment execution time would be penalized by the extra stack empty check To prevent this, two assignment codes are needed, Assign for single assignment and AssignList for multiple assignment.

To implement two assignment codes in the Translator, at the first equal, the token will be changed to Assign as previously planned. If the mode is Equal (indicating another equal in a multiple equal assignment), the Assign token on top of the hold stack will be changed to AssignList. If the mode is Comma, then the token will be changed to AssignList before pushing the token onto the hold stack. At the time the assignment token is added to the output list, the Assign operator will expect two operands (the first a reference) and the AssignList operator will expect multiple reference operands and the value to assign operand.

This brings up another issue. The Recreator will need to distinguish if the AssignList is from a multiple equal or comma separated multiple assignment so that the original code is recreated as it was entered. There could be two different AssignList codes for each (for a total of three assignment operators). Though not implemented yet, there will also need to be unique codes each assignment if the optional LET command word is entered (that's now 6 unique assignment codes). All these unique codes would not be required at run-time (only two are needed, single or multiple). There's actually a better way to prevent this multiplying of codes, but this will wait until the internal code is developed (and it will also eliminate the need for the dummy parentheses codes in the program, but not all the code needed to determine when it is needed).