Generic_Assignment

 An interface block can be used to define generic assignment.  The
 only procedures allowed in the interface block are subroutines that
 can be referenced as defined assignments.  Statement format for
 initial line in block:

    INTERFACE ASSIGNMENT(=)

 The subroutines within the interface block must have two
 nonoptional arguments, the first with intent OUT or INOUT, and the
 second with intent IN.

 A defined assignment is treated as a reference to a subroutine.
 The left side of the assignment corresponds to the first dummy
 argument of the subroutine; the right side of the assignment
 corresponds to the second argument.

 The ASSIGNMENT keyword extends or redefines an assignment operation
 if both sides of the equal sign are of the same derived type.

 Any procedure reference involving generic assignment must be
 resolvable to one specific procedure; it must be unambiguous.

 EXAMPLES:

   INTERFACE ASSIGNMENT (=)
     SUBROUTINE BIT_TO_NUMERIC (NUM, BIT)
     INTEGER, INTENT(OUT) :: NUM
     LOGICAL, INTENT(IN)  :: BIT(:)
     END SUBROUTINE BIT_TO_NUMERIC

     SUBROUTINE CHAR_TO_STRING (STR, CHAR)
     USE STRING_MODULE                    ! Contains definition 
                                          !   of type STRING
     TYPE(STRING), INTENT(OUT) :: STR     ! A variable-length string
     CHARACTER(*), INTENT(IN)  :: CHAR
     END SUBROUTINE  CHAR_TO_STRING
   END  INTERFACE

 The following example shows two equivalent ways to reference
 subroutine BIT_TO_NUMERIC:

   CALL BIT_TO_NUMERIC(X, (NUM(I:J)))
   X = NUM(I:J)

 The following example shows two equivalent ways to reference
 subroutine CHAR_TO_STRING:

   CALL CHAR_TO_STRING(CH, '432C')
   CH = '432C'