private void addInterface(ImFunctionType signature) {
JimpleInterfaceBuilder iface = context.getJimpleOutput().newInterface();
iface.setPackageName(PACKAGE_NAME);
iface.setClassName(signature.interfaceName());
iface.extendsInterface("org.renjin.gcc.runtime.FunPtr");
JimpleMethodBuilder applyMethod = iface.newMethod();
applyMethod.setName("apply");
applyMethod.setReturnType(signature.getReturnType());