5.17 $TEST

$TEST is a writable, NEW-able ISV that is 1 if the most recently evaluated expression was true. Otherwise, returns 0.

$TEST is implicitly NEWed when entering a new stack frame for extrinsic functions and argumentless DO. $TEST is not implicitly NEWed when a new stack frame is entered with an argumented DO.

For single-line IF or ELSE expressions, you may use THEN to stack $TEST until the end of the line. All new code should employ THEN in this manner, as stacking $TEST prevents a wide range of coding errors that can be very challenging to detect and eliminate.

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