Refactorings are source-to-source program transformations which change program structure and organisation, but not program functionality. Documented in catalogues and supported by tools, refactoring provides the means to adapt and improve the design of existing code, and has thus enabled the trend towards modern agile software development processes. Refactoring has taken a prominent place in software development and maintenance, but most of this recent success has taken place in the OO and XP communities.In our project, we explore the prospects for 'Refactoring Functional Programs', taking Haskell as a concrete case-study. This paper discusses the variety of pragmatic and implementation issues raised by our work on the Haskell Refactorer. We briefly introduce the ideas behind refactoring, and a set of elementary functional refactorings. The core of the paper then outlines the main challenges that arise from our aim to produce practical tools for a decidedly non-toy language, summarizes our experience in trying to establish the necessary meta-programming infrastructure and gives an implementation overview of our current prototype refactoring tool. Using Haskell as our implementation language, we also offer some preliminary comments on Haskell programming-in-the-large.
We demonstrate the Haskell Refactorer, HaRe, and the Erlang Refactorer, Wrangler, as examples of fully-functional refactoring tools for functional programming languages. HaRe and Wrangler are designed to handle multi-module projects in complete languages: Haskell 98 and Erlang/OTP. They are embedded in Emacs (and gVim) and respect programmer layout styles.In discussing the construction of HaRe and Wrangler, we comment on the different challenges presented by Haskell and Erlang due to their differences in syntax, semantics and pragmatics. In particular, we examine the sorts of analysis that underlie our systems.Finally, drawing on our experience, we examine features common to functional refactorings, and contrast these with refactoring in the object-oriented domain.
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