A quick lesson on: What is IMP?

[SMcNeill]

I think the biggest problem with IMP is that folks think of it logically, and not programmatically. 

In logic, we can say something such as NOT TRUE = FALSE.  When coding, however, that statement doesn't hold true, *except in very limited situations*.

NOT -1 = 0.  In this case, -1 is TRUE and 0 is FALSE, so the statement NOT TRUE = FALSE is correct.

But what if we NOT a different value?

NOT -2 = 1.  In this case -2 is TRUE, and 1 *is also* TRUE. 

NOT (a true condition) is *ONLY* a FALSE condition, when that condition is -1.  In all other cases, it's still TRUE.

Logically, we think that NOT TRUE is FALSE, but when coding, that's only accurate in the limited condition that our truth value is -1.  One could break the logic down just as simple to:

IF A = -1 THEN
  'NOT A is FALSE
ELSE
    'NOT A is TRUE
END IF

----------------------------

IMP breaks down to the same type of simplified logic.  When dealing with A IMP B, it's:

IF A =-1 AND B = 0 THEN
  'A IMP B is FALSE
ELSE
    'A IMP B is TRUE
END IF