Implementation of option types and option destructuring in C using horrifying hacks. `some`'s comma could probably be cleaned up with a decltype extension.

option.c

#include <assert.h>
#include <stdlib.h>
#include <stdbool.h>
#include <stdio.h>

#define option(T, name) \
    typedef struct option_##name { \
        optionhdr hdr; \
        T val; \
    } option_##name; \
    static option_##name some_##name(T val) {\
        option_##name opt; \
        opt.val = val; \
        opt.hdr.ptr = &opt.val; \
        return opt; \
    } \
    static option_##name none_##name() { \
        option_##name opt; \
        opt.hdr.ptr = NULL; \
        return opt; \
    }

typedef struct optionhdr {
    void *ptr;
} optionhdr;

enum optionenum {
    NONE,
    SOME
};

void *unwrap(void *ptr)
{
    optionhdr *opt = ptr;
    if (opt->ptr == NULL) {
        assert(false);
    }
    return opt->ptr;
}

bool is_some(void *ptr)
{
    optionhdr *opt = ptr;
    return opt->ptr != NULL;
}

bool is_none(void *ptr)
{
    optionhdr *opt = ptr;
    return opt->ptr == NULL;
}

enum optionenum which(void *ptr)
{
    optionhdr *opt = ptr;
    return opt->ptr != NULL;
}

#define match(opt) \
    for (optionhdr _opt = opt.hdr, run = {(void*)0x1}; run.ptr; run.ptr = NULL) \
        switch (which(&_opt))

#define some(T, name) case SOME: for(T *p = (is_some(&_opt)? unwrap(&_opt) : NULL), name = *p; p; p = NULL)

#define none case NONE: for(bool run = is_none(&_opt); run; run = false)

option(int, int)

option_int woop(int i)
{
    if (i%2 == 0) {
        return none_int();
    }
    return some_int(i);
}

int main(int argc, char **argv)
{
    option_int foo;
    if (argc < 2) {
        foo = none_int();
    } else {
        foo = some_int(atoi(argv[1]));
    }
    match (foo) {
        some (int, bar) {
            match (woop(bar)) {
                some (int, baz) {
                    printf("%i\n", baz);
                }
                none {
                    printf("I'm allergic to even numbers :(\n");
                }
            }
        }
        none {
            printf("none :(\n");
        }
    }
}