A factor in a run-time expression can be any of the following:

       array-type-identifier array-constructor
       constant-identifier
       constructor of schema type or of types containing
          schema components
       (expression) [[ :: type-identifier ]]
       function-identifier [[ actual-parameter-list ]]
       NOT factor
       numeric-constant
       real-constant
       record-type-identifier record-constructor
       schema discriminant
       [[ set-type-identifier ]] set-constructor
       string-constant
       variable

  A factor in a compile-time expression cannot include the following:

       call to user-defined functions
       call to EOF and EOLN predeclared functions
       constructor of schema type or of types containing
          schema components
       schema discriminant
       variable