VMS Help FORTRAN, Statements, FUNCTION  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Begins a function subprogram.  Identifies the data type of the
  function and names the dummy arguments.  Format:

     [typ] FUNCTION nam[*m][([p[,p]...])]

     typ  Is a data type.  If you do not specify a data type,
          the data type of the function is implied from its
          name.  If the data type is CHARACTER, you can specify
          CHARACTER*(*) to indicate a passed length function
          type -- the function type assumes the length of its
          definition in the program unit invoking it.

     nam  Is a symbolic name for the function.  The name must be
          unique among all global names in the program.  The name
          is used as a variable within the function.  The value of
          the variable is returned to the caller of the function
          as the value of the function.

     m    Is an unsigned, nonzero integer specifying the length of
          the data type. It must be one of the valid length specifiers
          for "typ".  This length overrides the length specified or
          implied by the type.

     p    Is an unsubscripted variable name specifying a dummy
          argument.  The arguments must agree in order, number, and
          type with the actual arguments of the statement invoking
          the function.  A dummy argument must not be defined as an
          array with more elements than the actual argument holds.

  The array declarator for a dummy argument can itself contain
  integer values that are dummy arguments or are references to a
  common block, providing for adjustable size arrays in functions.
  The upper bound of the array declarator for a dummy argument can be
  specified as an asterisk, in which case the upper bound of the
  dummy argument assumes the size of the upper bound of the actual
  argument.  The size in a character string declarator for a dummy
  argument can be specified as an asterisk in parentheses -- in which
  case the size of the actual argument is passed to the dummy
  argument.

  The values of the actual arguments in the invoking program unit
  become the values of the dummy arguments in the function.  If you
  modify a dummy argument, the corresponding actual argument in the
  invoking program unit is also modified; the actual argument must be
  a variable if it is to be modified.

  If the actual argument is a character constant, the dummy argument
  can be either character or numeric in type, unless the name of the
  subprogram being invoked is a dummy argument in the invoking
  program unit.  If the actual argument is a Hollerith constant, the
  dummy argument must be numeric.

  The FUNCTION statement must be the first statement of a function
  subprogram, unless an OPTIONS statement is specified.  A function
  subprogram cannot contain a SUBROUTINE statement, a BLOCK DATA
  statement, a PROGRAM statement, or another FUNCTION statement.
  ENTRY statements can be included to provide multiple entry points
  to the subprogram.

                                 NOTE

          In a function, the function name identifier  refers
          to  the  return  value,  not  the  function itself,
          unless an argument list is present.  Therefore,  it
          is  not  possible to pass a function as an argument
          to another routine from inside the  function.   For
          example, consider the following:

             INTEGER FUNCTION RECURSIVE_FUNCTION
                .
                .
                .
             CALL OTHERSUB (RECURSIVE_FUNCTION)

          The reference to  RECURSIVE_FUNCTION  in  the  CALL
          statement passes the function return value, not the
          function itself.