Anonymous functions in C using GCC extensions.

lambda.h

#ifndef _LAMBDA_H
#define _LAMBDA_H

#define LAMBDA(stmt, ret, ... /*args*/) \
    ({ ret __fun__(__VA_ARGS__) { stmt; }; __fun__; })

#endif

test.c

#include <stdio.h>

#include "lambda.h"

int main()
{
    void (*fun) (int, int) = LAMBDA(
        printf("%d + %d == %d", a1, a2, a1 + a2),
        void,
        int a1, int a2
    );
    
    fun(123, 456);

    return 0;
}