Not smart contracts exactly but there is a specific part of each bond called the waterfall (basically specifies what happens with all the cashflows under different circumstances and is a little bit like an equity cap table plus liquidity preferences). I've always thought there should be a dsl specifying the waterfall that can be used for the bond model and used to generate the legalese in the prospectus. A common problem is the bond model doesn't match the prospectus and that problem would just disappear. I intend to do this as a research project if I ever get time (it's been 12 years since I had the idea to do this so it may never happen...).