Chapter 1 Formalisation of Haskell

Abstract: Refactoring is a technique for improving the design of existing pro-grams without changing their external behaviour. HaRe is the refactoring tool we have built to support refactoring Haskell 98 programs. Along with the develop-ment of HaRe, we have also investigated the formal specification and proof of validity of refactorings. This formalisation process helps to clarify the meaning of refactorings, improves our confidence in the behaviour-preservation of refac-torings, and reduces the need for testing. This paper gives an overview of HaRe, and shows our approach to the formalisation of refactorings. 1.