Describing microservices using modern Haskell (experience report)

We present Mu, a domain specific language to describe and develop microservices in Haskell. At its core, Mu provides a type level representation of schemas, which we leverage in various ways. These schemas can be automatically imported from industry-standard interface definition languages. Mu uses many of the type level extensions to GHC, and techniques such as (data type) generic programming and attribute grammars. Apart from the description of the library, we discuss a series of shortcomings in current GHC/Haskell, mostly related to the friendliness of the exposed library interface once complex types enter the scene.