What has dependent type theory done for Haskell? In this talk, I will discuss the influence of dependent types on the design of programming languages and on the practice of functional programmers. Over the past ten years, the Glasgow Haskell compiler has adopted several type system features inspired by dependent type theory. However, this process has not been a direct translation; working in the context of an existing language has lead us to new designs in the semantics of dependent types. I will take a close look at what we have achieved in GHC and discuss what we have learned from this experiment: what works now, what doesn’t work yet, and what has surprised us along the way.