A polymorphic function is one that can operate on different types[1]. You would maybe be familiar with them as template functions in C++, though where C++ compiles different versions of the template functions based on the parameters, we pass extra implicit parameters. The example above translates to something like the following in pure C:

    void* malloc_T(size_t sizeof_T, size_t alignof_T) {
        return malloc(sizeof_T);
    }

    int* i = (int*)malloc_T(sizeof(int), alignof(int));

In this case, since the compiler verifies that int is actually a type with known size (fulfilling `sized(T)`), it can generate all the casts and size parameters above, knowing they're correct.

[1] To anyone inclined to bash my definition of polymorphism, I'm mostly talking about parametric polymorphism here, though Cforall also supports ad-hoc polymorphism (name-overloading). The phrasing I used accounts for both, and I simplified it for pedagogical reasons.