public SignatureVisitor visitParameterType() {
		if (type != METHOD_SIGNATURE
				|| (state & (EMPTY | FORMAL | BOUND | PARAM)) == 0) {
			throw new IllegalArgumentException();
		}
		state = PARAM;
		SignatureVisitor v = sv == null ? null : sv.visitParameterType();
		return new CheckSignatureAdapter(TYPE_SIGNATURE, v);
	}