Translator – Expression Type Implementation

A new routine was implemented to handle getting the current data type of the expression processed so far. This routine is called when the unexpected end of expression occurs to get the data type so that the correct “expected ...” error can be reported, and is also called before pushing an opening parentheses token to the hold stack to set its data type (so that it can be carried through the rest of the expression).

Once the routine was working, it was simplified. First, the token on top of the hold stack is checked for an operator before looking for the other conditions (parentheses, internal functions, and tokens with parentheses). This reduced the number of tests overall. An empty hold stack causes a bug error since at least the Null token should be on the stack.

If the top hold stack token is the Null token, then the data type is obtained from the token on top of the command stack. This caused another problem with commands (more on this in the next post). If the top token is an opening parentheses, then its data type is used (which could be none). Otherwise the data type of the operator's operand is used (first operand for a unary operator, second operand for binary operator).

If the top token on the hold stack is not an operator, then the top of the count stack is used to determine where to get the data type. If the count stack is empty, a bug error is returned since this situation should not happen. If the top is an internal function, then the data type of the current operand of the function is used. If the top is a parentheses, a bug error is returned since this situation should also not happen (parentheses token should have been on top of the hold stack). Otherwise the top contains a token with parentheses (an array or non-internal function) where the data type cannot be determined, so is set to None.