Translator – Sub-String Assignments

There will be several associated codes for assigning strings from a reference string or temporary string to a reference string or to a sub-string. The Encoder will determine which code to use once the string type for each operand is determined. For the Encoder to know if a sub-string is present, a new SubStr data type is needed, which only the LEFT$, MID$ and RIGHT$ functions return.

The Translator will check to make sure that sub-string assignments are valid by making sure the string argument is a reference string, at least if it is a Paren or NoParen token type. If it turns out to be a user function, then the Encoder will report the error. The Translator will also make sure that a compound sub-string assignment like LEFT$(RIGHT$(B$,3),2)="AB" is not entered.

The find code routine needs to handle sub-strings where the operands are popped off of the done stack and the reference flag is checked. For the first operand (last operand popped), if the data type of the token is SubStr (indicating a sub-string function) and the operand is a String, then the token's reference flag is set to operand's reference flag (the reference flag is transferred).  The operand's reference flag is then cleared as it is currently implemented. This assumes that the first argument of the sub-string function is the string being assigned.

If the operand's data type is anything but String (SubStr or TmpStr), then the reference flag is not transferred. For the invalid compound sub-string assignment, since the data type of the operand will be SubStr, the reference flag of the function's token will not be set. When the reference flag is checked for an assignment operator, the reference flag will only be set if the string operand was reference, otherwise if won't be set and an error will be returned.