Table – Encode Virtual Function

The encode mechanism needed to be improved.  The encode function in the program model converts an RPN list to a program line.  For each token in the RPN list, the first program word is generated from the code index and sub-codes of the token and added to the program line.  If the code in the token has an operand (using the is code with operand access function), the second program word is generated by calling the encode function of the table entry to get a index, which is added to the program line.

This mechanism was not making effective use of polymorphism.  A better way is to call the encode function for the table entry, which generates the one or two program words dependent on the requirements of the code in the token (via its table entry).  This was accomplished with several changes.

An encode function was added to the token class since the contents of the token are used for encoding.  The first argument is a pointer to the program unit (an instance of the program model class) needed for the codes with operands to access the dictionaries.  This function also needed access to the program line being encoded.  This was handled by passing a C++11 STL back inserter iterator as the second argument.  This iterator is used to add words to the program line, such as:

*backInserter = <ProgramWord>;

The token encode function then calls the encode function for the table entry.  The arguments include the program unit pointer, back inserter iterator and a pointer to the token.  A plain token pointer is passed (the this pointer).  The token argument of the entry encode functions were changed from a standard shared token pointer to a plain pointer (a shared pointer is not necessary here anyway).  This changes propagated to the dictionary add functions and the dictionary info add element and set element functions.

With the table entry encode functions adding the operand words to the program line directly (via the back inserter iterator), a return value is no longer needed.  The default encode function does nothing since most codes don't require a second operand program word.  For codes with operands (REM, constants, variables, etc.), their encode functions call the dictionary add function whose index return value is added to the program line.

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