A Boolean function designator specifies a function that returns a Boolean value (a value of TRUE or FALSE).

<Boolean function designator>

──┬─<procedure identifier>─────────┬─┬─────────────────────────┬───────┤
  ├─<Boolean intrinsic name>───────┤ └─<actual parameter part>─┘
  └─<procedure reference variable>─┘

<Boolean intrinsic name>

Any of the names listed under Boolean Intrinsic Names.

The procedure specified by the procedure identifier or the procedure reference variable must be of type BOOLEAN.