Closure in gcc

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

typedef int (*FN)(int n);

struct ClosureData {
    int value;
    struct ClosureData *next;
};

FN summ(int x) {
    static struct ClosureData *closureData = NULL;
    int fn(int y) {
        struct ClosureData *next;
        int result;
        result = closureData->value + y;
        next = closureData->next;
        free(closureData);
        closureData = next;
        return result;
    };
    struct ClosureData *newData;
    newData = (struct ClosureData*)malloc(sizeof(struct ClosureData));
    if (!newData) {
        while (closureData) {
            newData = closureData->next;
            free(closureData);
            closureData = newData;
        }
        fprintf(stderr, "System error: can't allocate memory.\n");
        exit(1);
    }
    newData->value = x;
    newData->next = NULL;
    if (!closureData) {
        closureData = newData;
    } else {
        closureData->next = newData;
    }
    return fn;
}

int main(int argc, char *argv[]) {
    printf("Summ: %d\n", summ(2)(3)); // 5
    printf("Summ: %d\n", summ(4)(4)); // 8
    return 0;
}