Written July 2023
Although BOOLEAN is an alias for I,2 (signed integer), declared in ashinc:types.def, it is intended to store only two possible values: .TRUE (-1) or .FALSE (0). (.TRUE and .FALSE are system-defined dot variables.) Note that an IF test will treat any non-zero value in any numeric variable type or expression as logically true, but using the BOOLEAN type and .TRUE (instead of, say, 1) to indicate logical truth allows for the NOT operator to work both arithmetically (flipping all the bits) and logically (flipping true and false), as expected.
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