Translator – Operands of Sub-Strings

One final issue was noticed with the eighth (Sub-String Assignments) Translator test that needed to be corrected, which can be seen with these sample statements (and their current translations):

A$ = LEFT$(B$, 1)  A$<ref> B$ 1 LEFT$([B$] Assign$
A$ = LEFT$(B$+C$, 2)    A$<ref> B$ C$ +$[B$,C$] 2 LEFT$([+$] Assign$

In these examples, remember that the Translator cannot determine if B$ and C$ are variables or functions, therefore these operands are attached to the code they belong to so that the Encoder can adjust the operators and functions accordingly with associated codes with the appropriate arguments. However, sub-string functions add a wrinkle to this scheme.

During run-time, sub-string functions work the same whether their string operand is a reference or a temporary string – they will simply modify the string pointer and length of the string on top of the evaluation stack. Temporary strings are not deleted since the sub-string refers to the temporary string – whichever code has the sub-string function as an operand will take care of deleting the temporary strings. Only be one code for each sub-string function is needed (not two, one with a reference string and one with a temporary string as an operand). The correct translations of the statements above should be:

A$ = LEFT$(B$, 1)  A$<ref> B$ 1 LEFT$( Assign$[B$]
A$ = LEFT$(B$+C$, 2)  A$<ref> B$ C$ +$[B$,C$] 2 LEFT$( Assign$[+$]

In the first statement, the B$ should be attached to the Assign$ token so that the Encoder can change it to an AssignStrTmp code if B$ turns out to be a function (results of functions are  temporary strings) or leave it the AssignStr code if it is a variable. In the second statement, the Translator can change it to an AssignStrTmp code with no attached token, but until temporary strings are fully support, it will attach the +$ to an AssignStr code.

Since the result of a sub-string function is the same as its operand (reference or temporary string), the operands of the sub-string function simply get transferred to the token that has the sub-string function as an operand.