Ftcl: Calling Tcl procedures

The interface: Fortran calling Tcl

Fortran routines may use the following routines to interact with the Tcl interpreter (cf. Technical details):

Set the value of a Tcl variable:
call ftcl_put( variable, value )
The argument variable is the name of the Tcl variable to be set and value is an argument of type integer, real, logical, double precision or a character string.
Note:
If the variable does not yet exist, it will be created.
Retrieve the current value of a Tcl variable:
call ftcl_get( variable, value )
The argument variable is the name of the Tcl variable to be retrieved and value is an argument of type integer, real, logical, double precision or a character string.
Notes:
- If the variable does not exist, then a default value is returned.
- If the value to be returned is a character string, the longest string that will be returned is determined by the actual Fortran string argument. For instance:
  In Tcl:
  set string "1234567890"
  In Fortran:
  character*2 str ... call ftcl_get( 'string' , str ) write(*,*) 'Result: >', str, '<'
  would print:
  Result: >12<
Set the contents of an array:
call ftcl_put_array( listname, array )
The argument listname is the name of the Tcl list to be set and array is a one- or two-dimensional array of type integer or real.
Note:
On the Tcl side this becomes a list or a list of lists, whose length corresponds to the dimension of the Fortran array argument.
Retrieve the contents of an array (a Tcl list):
call ftcl_get_array( listname, array )
The argument listname is the name of the Tcl list to be retrieved and array is a one- or two-dimensional array of type integer or real.
Note:
On the Tcl side this should a list or a list of lists, whose length corresponds to the dimension of the Fortran array argument.
Execute a Tcl script:
call ftcl_script( string )
The argument string must be a valid Tcl command stored in a single character string.
Set the configuration parameters:
call ftcl_config( option, value )
The argument option must be one of the following: to be implemented.
Set the result string:
call ftcl_set_result( value )
The argument value is either an integer, real, double precision real, logical or string.
Set the error code:
call ftcl_set_error( error )
The argument error is a logical value, .TRUE. indicating some error was discovered (the result string should explain what happened), .FALSE. indicating everything was fine.

Note: The routines to manipulate Fortran arrays have not been implemented yet.

Creating a graphical user-interface with Tk

The Ftcl library makes it possible to create user-interfaces using the Tk extension. Here is a small example (see also the lander sources in the distribution):

      PROGRAM LANDER

      USE FTCL

      CHARACTER(80) astring

      IMPULSE = 200
      FHEIGHT = 10000.0
      SPEED = 100.0
      FUEL = 1000.0
      GROSS = 900.0

      CALL ftcl_start('config.tcl')
      CALL ftcl_script('package require Tk')
      CALL ftcl_script('inputInitialValues')
      CALL ftcl_script('update')
      CALL ftcl_script('update idle')

      CALL ftcl_get_string('burn', astring)

      CALL ftcl_get_int('ready', irdy)

      DO WHILE (irdy == 0)
        CALL ftcl_script('update')
        CALL ftcl_script('update idle')
        CALL ftcl_get_int('ready', irdy)
      ENDDO
      CALL ftcl_get_real('burn', burn)
      I = 0

      DO WHILE (FHEIGHT .GT. 0)
        CALL ftcl_get_real('burn', burn)
        CALL CALCSPEED (SPEED, FUEL, GROSS, BURN, IMPULSE, SPEED)
        I = I + 1
        FUEL = FUEL - BURN
        IF (FUEL .LE. 0)  THEN
          FUEL = 0
          BURN = 0
        CALL ftcl_put_real('burn', burn)
        ENDIF
        FHEIGHT = FHEIGHT - SPEED
        CALL ftcl_put_int('time', I)
        CALL ftcl_put_real('speed', speed)
        CALL ftcl_put_real('fuel', fuel)
        CALL ftcl_put_real('ht', FHEIGHT)
        CALL ftcl_script('showState')
        CALL ftcl_script('update idle')
      ENDDO

      DO
        CALL ftcl_script('update idle')
        CALL ftcl_script('update')
      ENDDO

      END

      SUBROUTINE CALCSPEED (finit, fuel, gross, burn, impulse, speed)
      MASS = gross + fuel
      SPEED = SPEED + 9.8 * (1 - impulse * log(mass/(mass-burn)))
      END

This program consists of the following steps:

It loads the Tk extension (via "package require Tk")
It sets up the user-interface elements (defined via the file "config.tcl")
It runs the commands "update" and "update idletasks" to make sure the user-interface can be shown on screen
It then enters a loop to see if the user wants to run the program (irdy is set by the Go button)
If the button was pressed, it enters a second loop to do the computation (the height and speed and so on of a lunar lander are computed) and updates the user-interface.
Finally, when the computation is done, it runs an idle loop to allow the user to view the result.

Because the Fortran program stays in control, it is necessary to use the update command, so that window and other events can be handled properly.

An alternative is to use the ftcl_make_command() routine to register a new Tcl command (implemented in Fortran) and to enter the event loop, as normally happens in applications using Tk (such as wish), via ftcl_main_loop().