Translator – Operators

As mentioned, operator tokens are pushed onto an operator stack after pulling higher precedence operators off of the operator stack and adding them to the RPN list. However, there is some handling that needs to be performed before an operator can be added to the RPN list.  For each operator, the Translator needs to check the data type of the operator's operand to be sure they are compatible with the operator and/or to add the proper operator dependent on the data types of the operands.

Take the + operator, which can have integer, double or string operands. If both operands are strings, then the concatenation operator needs to be added. For numeric values, it's a bit more involved. If both the operands are integers, then an add integer operator is added. If both the operand are doubles, then an add double operator is added. For an integer and a double, the result will be a double, but the operand that is an integer (which could be the first or the second operand) needs to be converted to a double before performing an add double operator.

The goal is for optimal execution, so having the add double operator check to see if the one of the operands is an integer that needs to be converted first during run time is not ideal. This check should be done before hand. If a conversion is needed, an internal integer to double conversion operator will be inserted into the code.  So, for the expression A% + B, the internal code will be A% CvtDbl B +. During run time, the CvtDbl will operate like a function or unary operator, when A% is pushed onto the run-time stack, the CvtDbl will pop it off the stack, convert it to double and push the double value back on the stack.

The Translator will insert these hidden operators into the RPN list after the appropriate operand as needed by the operator.  (This is why the List class was modified to have append and insert functions – see post List Class – Updated.) When the internal code is output by the Recreator, these hidden operators will not produce any output.