HOPL

               A SIMPLE EXAMPLE

# include "macros.h"

@@ LOGUNIT     - manage Fortran Logical unit numbers

# define MaxUnits     30
# define LowUnit     60

     module logunit

     logical un(MaxUnits)     @ Is unit number in use?

     blockdata inilogun
     data un = MaxUnits * f
     end

@+ gtlun     - get a free logical unit number

     subroutine gtlun( num )
     integer num     @* free logical unit number returned

@-     general, system
@! 2/91, GAC: Written

     integer i          @ do loop index
     external inilogun     @ invoke blockdata for linker

     do i = 1, MaxUnits
          if (un(i)) cycle
          num     = i + LowUnit - 1
          un(i)     = t
          return
     end do
     FatalCheck(t, 'Too many logical unit numbers')
     end

@+ frlun     - free a Fortran logical unit number

     subroutine frlun( num)
     integer num     @ unit number to be freed

@-     general, system
@! 2/91, GAC: Written

     integer i     @ temporary index

     i     = num - LowUnit + 1
     FatalCheck(i < 1 || i > MaxUnits, 'Illegal logical unit number')
     FatalCheck(^ un(i), 'Logical unit number never given out')
     un(i)     = f
     end

     end module

NOTES:
1. The comment symbol arrangement in position 1 with the following
   special symbols may give an indication of an embryonic documentation
   standard.
2. Fatalcheck is, of course, a macro, and allows you to postpone the
   decision of how to react to errors.

CAP(ID:7775/)

Fortran preprocessor