lambda-test.c

/*
 * Anonymous functions using GCC statement expressions. (from http://stackoverflow.com/questions/10405436/anonymous-functions-using-gcc-statement-expressions)
 *
 * They capture variables, too!
 *
 * Output:
Timer at 0x7fffffffde70
Callback w/ cookie 0x7fffffffde70, truth 42.
 */

#include <stdio.h>

#define lambda(return_type, function_body) \
({ \
      return_type __fn__ function_body \
          __fn__; \
})

typedef void (*callback_t)(void *);

typedef struct {
    void *data;
    int started;
    callback_t callback;
} timer_t;

void start(timer_t *t, void *data, callback_t callback)
{
    t->data = data;
    t->callback = callback;
}

void run(timer_t *t)
{
    t->callback(t->data);
}

void second(timer_t *t)
{
    run(t);
}

int main(int argc, char **argv)
{
    int truth = 42;
    timer_t timer;
    printf("Timer at %p\n", &timer);

    start(&timer, &timer, lambda (
        void, (void *cookie) {
            printf("Callback w/ cookie %p, truth %d.\n", cookie, truth);
        }));

    second(&timer);
}