Как передать параметр CALLBACK функцию???

typedef int   (CALLBACK * PCLOSURE)         (HWND hwnd, void (CALLBACK *Fn), LPARAM UI, LPSTR pwd, char type);

extern PCLOSURE         Closure;

void CALLBACK _export PrinterResults(struct RetData far &rtd) {}

Closure(NULL, PrinterResults, 0, "0", '2');

[DllImport("f.dll", EntryPoint = "Closure")]
unsafe public static extern int Closure(void* hwnd, void* Fn, int UI, string pwd, char type);

Closure(null, null, 0, "", '2');