m_sdl.c

#include <stdio.h>
#include <SDL2/SDL.h>
#include <gtmxc_types.h>

void m_SDL_Init(int c, gtm_ulong_t flags, gtm_long_t* result) {
    printf("Calling SDL_Init with 0x%lx... ", flags);
    *result = SDL_Init(flags);
    printf("Done!\n");
    fflush(stdout);
}

m_sdl.xc

$PWD/m_sdl.so
init: void m_SDL_Init(I:gtm_ulong_t, O:gtm_long_t*)

Rakefile

file 'm_sdl.so' => 'm_sdl.c' do
  sh 'gcc -shared -fpic -o m_sdl.so -Wall -Werror -std=gnu99 m_sdl.c -I/opt/gtm -O3 $(sdl2-config --cflags --libs)'
end

file 'trumps.o' => 'trumps.m' do
  sh 'mumps trumps.m'
end

task :run => ['trumps.o', 'm_sdl.so'] do
  sh 'env GTMXC_sdl=m_sdl.xc mumps -run trumps'
end

task :clean do
  sh 'rm -rf *.o *.so'
end

task :default => :run

sdl.m

sdl

InitVideo() quit 32

init(flags)
 do &sdl.init(flags,.result)
 quit result

trumps.m

 write $$init^sdl($$InitVideo^sdl)