Network Protocol Programming in Haskell

Over seven years, we have developed several network protocol libraries including anti-spam, DNS, HTTP/1.1, HTTP/2 and TLS 1.3 in Haskell. Based on these experiences, we regard Haskell as a safe and highly-concurrent network programming language thanks to its strong type system and lightweight threads (i.e. green threads). This paper describes advantages and disadvantages of Haskell and reports our experiences. Haskell is typically described as a purely functional programming language. Unfortunately, this catch-phrase gives programmers an impression that is difficult to approach. Roughly speaking, pure means that Haskell’s type system clearly separates pure functions (i.e. without side effects) and impure functions (i.e. with side effects), and prevents pure functions from calling impure functions. Functional indicates that Haskell encourages modular programming with immutable data which provides consistency for concurrent programming.