Servant

Servant is a popular web framework based on the programming language Haskell, with an emphasis on data type safety. Servant provides a type-level domain-specific language (DSL) to describe World Wide Web application programming interfaces (Web APIs); various interpretations of such descriptions are possible: as a server, which dispatches requests to handlers; as documentation and schema specifications for the API; and as client libraries in various languages. It is used in production by companies such as GitHub, NoRedInk, Klarna, Input Output Global Inc. (in the Cardano project), and Wire. It is free and open-source software released under a BSD 3-clause license. The type-level approach pioneered by Servant allows extensibility along the dimensions of both data and behavior, and is thus a solution to the expression problem. New combinators or terms in the DSL can be modularly introduced, as can new interpretations of them, as entirely separate packages. As of 2023, well over 100 packages related to Servant have been published in the Haskell package repository. See also Yesod (web framework) Snap (web framework)