Off the top of my head, some results would be:
1. No one wants to lend to your country again because you paid them back with currency far less valuable than expected
2. Nobody wants to use your currency as a means of exchange in international transactions because it can fluctuate suddenly
3. Massive redistribution of wealth from savers and lenders to borrowers (maybe a good thing on the whole, but devastating for people headed into retirement)
4. Anything (including govt. programs) that aren't indexed to inflation are suddenly far less valuable