CHECKEXIST Operator

The format of the CHECKEXIST operator is:

When an object is activated, it also activates its attributes. If one of its attributes is its length, say, this attribute is included in the ElementList, and arrives in an elevated existence state at the CHECKEXIST operator. The CHECKEXIST operator sends the value of the attribute out on CheckItem?, and observes the return value of CheckOK@. If the return value is False (the attribute did not meet the test) then an existence value of UKE 0.5 (Ignore) is driven back down the connection to the attribute, potentially turning off the object that was activated, as one of its attributes did not meet requirements.

In logical terms,

    IF Object.Activated THEN IF Object.Length > 50 THEN...

except here, the test is dealing with a family of objects, and will only be activated if the object is, after it passes through whatever existence checks on it are necessary.

Another use could be as string checking, as

See     ATTRIBUTES
            MEMBERS