Parser – Negative Constants

Negative constants were previously not considered by the Parser, which interpreted a minus as the subtract operator. The Translator then changed it to a negate operator when it appeared in the operand state. Consider these two examples (along with there current translations):

A = B-1.5      A B 1.5 Sub Assign
A = -1.5+B     A 1.5 Neg B Sub Assign

The reason for the Parser to not look for signs on numerical constants can be seen in the first example. If the Parser produced the four tokens A = B -1.5, the Translator would generate an “expected operator” error at the -1.5 token since a second operand token was received when it was expecting a binary operator. The second example produces an unnecessary negate token after the constant. While perfectly valid, this is not desirable.

In order for the Parser to correctly interpret negative signs on numerical constants, it needs to be aware of whether the Translator is in operand state or not. If in operand state, the Parser can look for a negative sign in front of a number constant, otherwise a minus should be interpreted as an operator.

A new operand state flag was added to the Parser with an access function to set its value (which is initialized to off). The Parser get number routine was modified to have a new sign flag used to determine if a negative sign was found first. This flag will also prevent multiple negative signs. However, it will only check for a negative sign if no digits or a decimal was seen and if the new operand state flag is on.

An access function was added to the Translator to get the current operand state (either operand or operand-or-end state). Before calling the Parser get token routine, the Parser operand state is set from the Translator's current operand state. While testing, a problem was discovered with unary operators...