fortran-tcl86 – Tcl/Tk 8.6 for Fortran 2018

A work-in-progress Fortran 2018 ISO_C_BINDING interface library for interoperability with Tcl/Tk 8.6. This library allows you

to embed Tcl into Fortran,
to create Tcl extensions in Fortran (with Tcl Stubs),
to access (a subset of) the Tcl/Tk C API from Fortran,
to use Tcl as an evaluatable configuration file format, and
to add graphical user interfaces to Fortran programs.

There are some smaller differences to the original API:

Procedure names have been converted from camel case to snake case (for example, tcl_eval_ex() in Fortran instead of Tcl_EvalEx() in C).
Character strings passed to library procedures do not have to be null-terminated, as this step is done by Fortran wrappers.
Types are converted to their Fortran counter-parts (such as logical instead of c_int for boolean values).
Some procedure arguments have been made optional to avoid passing of c_null_ptr, c_null_funptr, and 0.
The interfaces called by the wrapper procedures contain a trailing underscore _ in their name (for example, wrapper tcl_eval() appends a null character to the second argument, then calls Fortran interface tcl_eval_()).
Functions and routines exposed to Tcl must have the bind(c) attribute.

See COVERAGE for a table of the bound procedures.

Fortran Libraries

Library	Description
`libftcl86.a`	Bindings to Tcl (`libtcl86`)
`libftclstub86.a`	Bindings to Tcl Stubs for extensions in Fortran (`libtclstub86`)
`libftk86.a`	Bindings to Tk (`libtk86`)

Build Instructions

Tcl 8.6 and Tk 8.6 with development headers have to be present. On FreeBSD, install the packages with:

# pkg install lang/tcl86 x11-toolkits/tk86

You will also need a Fortran 2018 and a C compiler. Then, execute the provided Makefile to build the static Fortran interface libraries libftcl86.a, libftclstub86.a, and libftk86.a:

$ make

By default, gcc and gfortran are used for compilation, but you can override the settings:

$ make CC=icc FC=ifort

Furthermore, it is possible to build a single static library libfortran-tcl86.a with fpm:

$ fpm build --profile=release --c-flag="`pkg-config --cflags tcl86`"

The include and library search paths in --c-flags have to point to the correct directories.

Linking Tcl & Tk

Linking depends on whether Fortran is called from Tcl or Tcl from Fortran. To build a Fortran program in example.f90 that invokes the Tcl interpreter, link against libftcl86.a -ltcl86:

$ gfortran -I/usr/local/include/tcl8.6/ -L/usr/local/lib/tcl8.6/ \
  -o example example.f90 libftcl86.a -ltcl86
$ ./example

The include and library search paths as well as the name of the Tcl 8.6 library itself may have to be changed depending on your operating system (-ltcl8.6 instead of -ltcl86 on Linux). Tcl/Tk can either be linked statically (libtcl86.a, libtk86.a) or dynamically (-ltcl86, -ltk86).

To create a shared library libexample.so with Tcl extensions written in Fortran, run:

$ gfortran -DUSE_TCL_STUBS -fPIC -shared -o libexample.so `pkg-config --cflags tcl86` \
  example.f90 libftcl86.a libftclstub86.a `pkg-config --libs tcl86`

To access the Tk toolkit from Fortran, link against libftk86.a libftcl86.a -ltk86 -ltcl86 (or, use pkg-config):

$ gfortran -DUSE_TK_STUBS `pkg-config --cflags tk86` \
  -o example example.f90 libftk86.a libftcl86.a `pkg-config --libs tk86`
$ ./example

Example

The following basic example just invokes the Tcl interpreter from Fortran to evaluate a character string:

! example.f90
program main
    use, intrinsic :: iso_c_binding, only: c_associated, c_ptr
    use :: tcl
    implicit none (type, external)

    integer     :: rc
    type(c_ptr) :: interp

    ! Create Tcl interpreter.
    interp = tcl_create_interp()
    if (.not. c_associated(interp)) stop 'Error: Tcl_CreateInterp() failed'

    ! Evaluate string as Tcl command.
    rc = tcl_eval_ex(interp, 'puts "Hello, from Tcl!"')
    if (rc /= TCL_OK) print '("Error: Tcl_EvalEx() failed")'

    ! Delete Tcl interpreter.
    call tcl_delete_interp(interp)
end program main

Compile and link the example with:

$ gfortran `pkg-config --cflags tcl86` -o example.f90 libftcl86.a `pkg-config --libs tcl86`
$ ./example
Hello, from Tcl!

Further Examples

The following example programs are provided:

config – Uses Tcl as a configuration file format (run config).
dict – Shows dictionary access (run dict).
eval – Evaluates a script in the Tcl interpreter (run eval).
fs – Tests Tcl file system API procedures (run fs).
library – Creates a Tcl extension hello inside a shared library (run script.tcl).
link – Demonstrates shared access to a variable between Tcl and Fortran (run link).
namespace – Creates a Tcl extension ::fortran::hello (with namespace) inside a shared library (run script.tcl).
re2c – Shows a Tk window to convert temperature values by calling an extension written in Fortran (run re2c).

To build the examples, run:

$ make examples

Change to the directory of an example before executing it.

Licence

ISC

interkosmos / fortran-tcl86