Multiple String Assignments – With Sub-Strings

Multiple string assignments will be handled by the AssignListStr code.  At run-time, this code (as the other assign list codes) will pop the value to be assigned from the stack and then begin popping variable references from the stack, assign the value, and continue until the stack is empty.  This will not work if any of the references to assign is a sub-string.  With the old design, mix-string assignments were handled with the AssignListMixStr code.  This was detailed in the post on May 22, 2010, but no details were given how this would be handled at run-time.

For the new design, if a multiple string assignment contains at least one sub-string, then there will be a specific assign code for each assignment instead of a single assign list code.  The specific assign codes will keep the value being assigned on the stack for the next assign code.  Only the last code will be a regular assign code.  Consider this mixed string assignment and its translation (note color coding showing the tokens that the codes process):

A$, LEFT$(B$,5), RIGHT$(C$,2) = D$
A$ B$ 5 C$ 2 D$ AssignKeepRight AssignKeepLeft AssignStr

The assign keep codes will pop the value to be assigned from the stack, pop the reference to assign, assign the value to the reference and push the value back to the stack for the next assign code.  The final regular assign code will not push the value to be assigned back to the stack leaving the stack empty.

There will be five assign keep codes: AssignKeepStr, AssignKeepLeft, AssignKeepMid2, AssignKeepMid3 and AssignKeepRight.  In the table, these codes will be the second associated code for the AssignStr, Left, Mid2, Mid3 and Right code entries.