psync.c

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

typedef struct psync_state {void *lbl; void *data;} psync_state;

#define CONCAT1(a, b) a ## b
#define CONCAT2(a, b) CONCAT1(a, b)

#define PDECL(ret, name, ...) \
    typedef ret name ## _ret; \
    psync_state name(psync_state _psync_st, __VA_ARGS__)

#define _PSTRUCT(var)   typeof(var) var;
#define _PASSIGN(var) var = _psync_args->var;
#define _PCOMMA(var)  var,

#define _PSTVAR(_) _(_psync_call)

#define PINIT() \
    psync_state _psync_call; \
    struct _pstruct {PVARS(_PSTRUCT) _PSTVAR(_PSTRUCT)} *_psync_args; \
    if(!_psync_st.lbl){ \
        _psync_args = malloc(sizeof(struct _pstruct)); \
    }else{ \
        _psync_args = _psync_st.data; \
        PVARS(_PASSIGN) \
        _PSTVAR(_PASSIGN) \
        goto *_psync_st.lbl; \
    }

#define PWAIT(lbl) \
    *_psync_args = (struct _pstruct){PVARS(_PCOMMA) _PSTVAR(_PCOMMA)}; \
    return (psync_state){&&lbl, _psync_args}; \
    lbl:

#define PCALL(func, ...) ({ \
        _psync_call = (psync_state){0}; \
        _psync_call = func(_psync_call, __VA_ARGS__); \
        while(_psync_call.lbl){ \
            PWAIT(CONCAT2(func, CONCAT2(_call_, __COUNTER__))); \
            _psync_call= func(_psync_call, __VA_ARGS__); \
        } \
        *(func ## _ret*)_psync_call.data; \
    })

#define PRET(var) \
    *(typeof(var)*)_psync_args = var; \
    return (psync_state){0, _psync_args};

PDECL(int, add, int, int);

PDECL(int, add, int a, int b) {
    int c;
#define PVARS(_) _(a) _(b) _(c)
    PINIT()
    c = 0;
    c += a;
    PWAIT(add_b)
    c += b;
    PRET(c)
#undef PVARS
}

PDECL(int, add3, int a, int b, int c){
    int d;
#define PVARS(_) _(a) _(b) _(c) _(d)
    PINIT()
    d = 0;
    d = PCALL(add, d, a);
    d = PCALL(add, d, b);
    d = PCALL(add, d, c);
    PRET(d);
#undef PVARS
}

int main(void){
    struct psync_state st1, st2;
    st1 = add3((psync_state){0}, 10, 25, 13);
    st2 = add3((psync_state){0}, 100, -30, 25);
    while(st1.lbl || st2.lbl){
        if(st1.lbl) st1 = add3(st1, 0,0,0);
        if(st2.lbl) st2 = add3(st2, 0,0,0);
    }
    printf("1: %d\n", *((add3_ret*)st1.data));
    printf("2: %d\n", *((add3_ret*)st2.data));
    free(st1.data);
    free(st2.data);
}