Nepal does not yet have a constitution. It is ruled under the Interim Constitution of 2007 which was instituted when the monarchy was abolished. This constitution was meant to oversee the transition of Nepal from a unitary,constitutional monarchy to a federal republic. Since then, Nepalese political parties have been trying to draft a final Constitution but have failed to do so. A new Constitution is supposed to be finalized in 2015.
The main difference between the pre-2007 Constitution of Nepal and the Constitution of India was that the Nepalese Constitution proclaimed that country to be a unitary constitutional monarchy. On the other hand, under the Indian Constitution, India is a federal republic.