Translator – Temporary Strings

The impact of temporary strings on the Translator is not much since the work of finding associated codes will be left for the Encoder. However, there are a few changes that are required – the main one is passing the operands to the Encoder so that it has easy access to them.

A new TmpStr data type will be added. The data type of the string operator (CatStr) and the internal functions that return a string will be changed to TmpStr.  This includes the internal functions CHR$, REPEAT$, SPACE$ and STR$. Something else is needed for the functions LEFT$, MID$ and RIGHT$, which will be revealed shortly. Any string DefFunP and DefFunN token types will also be changed to TmpStr since defined (one-line) string functions will return a temporary string during run-time.

The conversion code table used by the match code function needs to be expanded to include the new TmpStr data type. As far as the Translator is concerned, the String and TmpStr data types are the same, therefore the conversion code table entries for String to TmpStr and TmpStr to String will be set to the Null code.

For the string operator and internal string functions that have string operands, the operands need to be attached to the operator/function token within the output list. To accomplish this, the output list will be changed from a token pointer to a pointer to a new RpnItem structure that will contain the token pointer, the number of operands (0 if not applicable) and a pointer to an array of output list item (RpnItem) pointers.

There will be a new String flag added for these codes so that the Translator can easily identify them. When this flag is set, the number of operands will be set and the output list pointer array will be allocated. This array will be filled from the operands popped from the done stack. The done stack will also be changed to a stack of RpnItem structure pointers.

This saving of operands functionality is also needed for parentheses tokens, which can be arrays or user functions. The processing of array subscripts and user function arguments also needs to be delayed until the Encoder since the Translator doesn't know the difference between an array (whose subscripts all need to be integers) or a user function (whose argument types will be contained in the dictionary and defined in a function definition statement).