Awful Result/try! implementation in C

try.c

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

enum ResultKind { Kind_Ok, Kind_Err };

typedef struct {
    enum ResultKind kind;
    union {
        struct { int ok; };
        struct { char* err; };
    };
} ResultInt;

bool is_ok(ResultInt* r) {
    return (r->kind == Kind_Ok);
}

bool is_err(ResultInt* r) {
    return (r->kind == Kind_Err);
}

int get_ok(ResultInt* r) {
    assert(is_ok(r));
    return r->ok;
}

char* get_err(ResultInt* r) {
    assert(is_err(r));
    return r->err;
}

void print_result(ResultInt* r) {
    if (is_ok(r)) {
        printf("Ok(%i)\n", get_ok(r));
    } else {
        printf("Err(\"%s\")\n", get_err(r));
    }
}

ResultInt Ok(int ok) {
    ResultInt out;

    out.kind = Kind_Ok;
    out.ok = ok;

    return out;
}

ResultInt Err(char* err) {
    ResultInt out;

    out.kind = Kind_Err;
    out.err = err;

    return out;
}

#define TRY(var, r) {\
    if (is_ok(r)) {\
        *var = get_ok(r);\
    } else {\
        return *r;\
    }\
}

/* user code below */

ResultInt ensure_positive(int input) {
    if (input >= 0) {
        return Ok(input);
    } else {
        return Err("input was negative!");
    }
}

ResultInt mul_naturals(int a, int b) {
    int x, y;
    ResultInt result;

    result = ensure_positive(a);
    TRY(&x, &result);

    result = ensure_positive(b);
    TRY(&y, &result);

    return Ok(x * y);
}

int main() {
    ResultInt result;

    result = mul_naturals(2, 3);
    print_result(&result);

    result = mul_naturals(5, -6);
    print_result(&result);

    return 0;
}

try_output

Ok(6)
Err("input was negative!")