Following code causes booc to crash. class Foo: def Bar1(parameter as string): print "Something" return 5 def Bar2(): result = Bar1.BeginInvoke() Booc will crash if you try to compile it. It's a stack overflow. Boo is continuously trying to resolve Bar1.BeginInvoke to one of its overloads. Since no overload matches, it appears to continuously loop, loop, loop .. .. ..