I tried to create a window on Linux(as i undestand you need to use additional libraries in Linux) so i tried to reach the this code using CFFI command (cffi:foreign-funcall "main" :void :void :int) The C CODE: #include <GLFW/glfw3.h> #include <stdlib.h> #include <stdio.h> static void error_callback(int error, const char* description) { fputs(description, stderr); } static void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods) { if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS) glfwSetWindowShouldClose(window, GL_TRUE); } int main(void) { GLFWwindow* window; ... } Which works in C. But SBCL gives me error message: Execution of a form compiled with errors. Form: (EXTERN-ALIEN "main" (FUNCTION INT VOID)) Compile-time error: during macroexpansion of (EXTERN-ALIEN "main" (FUNCTION INT VOID)). Use *BREAK-ON-SIGNALS* to intercept. cannot use values types here [Condition of type SB-INT:COMPILED-PROGRAM-ERROR] What does this error mean? Can we call main function in C using CFFI? Is there a solution?