Servant is a domain-specific language embedded in Haskell that allows the specification of web APIs as Haskell types. From such an API type, various functionality can then be statically computed.
For example, for turning the API into a web server, the developer just has to provide a number of handlers. The type system ensures that the handlers are compatible with the specified API: every handler has to be present; handlers automatically get query parameters and the request body supplied in decoded form, as Haskell values of the right type, as specified by the API; handlers also have to provide a result of the correct Haskell type. There is no risk of run-time errors by mistakenly accessing a non-existing parameter or returning the wrong kind of result, because all coding and decoding is performed by Servant, as dictated by the API.
From a Servant API, one can also build a client, comprising functions that query each of the endpoints. Once again, Servant will take care of all the coding and decoding, allowing the client functions to work with proper Haskell types.
Further interpretations of the API type include documentation in various formats, mock servers, type-safe link generation, and more.
In the talk, we will introduce the idea of Servant and provide several examples of its use.
Andres Löh is a Haskell consultant and co-owner of Well-Typed LLP. He is based in Regensburg, Germany. He started using Haskell in 1997, when being an undergraduate student of mathematics in Konstanz, and has been an enthusiastic functional programmer ever since. Andres obtained a PhD in Computer Science from Utrecht University in 2004, on extending the Haskell language with capabilities for datatype-generic programming. After having been a university lecturer for several years, he joined Well-Typed in 2010.
Andres is very interested in applying functional programming to real-world problems, and in particular in datatype-generic programming, domain-specific languages, (dependent) type systems, parallel and concurrent programming, and the theory of version control.