Refactoring tools for functional languages

Abstract

Refactoring is the process of changing the design of a program without changing what it does. Typical refactorings, such as function extraction and generalisation, are intended to make a program more amenable to extension, more comprehensible and so on. Refactorings differ from other sorts of program transformation in being applied to source code, rather than to a 'core' language within a compiler, and also in having an effect across a code base, rather than to a single function definition, say. Because of this, there is a need to give automated support to the process. This paper reflects on our experience of building tools to refactor functional programs written in Haskell (HaRe) and Erlang (Wrangler). We begin by discussing what refactoring means for functional programming languages, first in theory, and then in the context of a larger example. Next, we address system design and details of system implementation as well as contrasting the style of refactoring and tooling for Haskell and Erlang. Building both tools led to reflections about what particular refactorings mean, as well as requiring analyses of various kinds, and we discuss both of these. We also discuss various extensions to the core tools, including integrating the tools with test frameworks; facilities for detecting and eliminating code clones; and facilities to make the systems extensible by users. We then reflect on our work by drawing some general conclusions, some of which apply particularly to functional languages, while many others are of general value.

Characterising renaming within OCaml’s module system: theory and implementation

“…Much work on refactoring has been carried out within the object-oriented programming paradigm; a standard reference is [12]. Thompson and Li have carried out a survey of refactoring tools for functional languages [42] including the tools Wrangler [23,24] (for Erlang [8]) and HaRe [25] (for Haskell [34]). Renaming, and perhaps refactoring generally, seems to be more diicult in a language like OCaml with its powerful module system.…”

D euce

“…While we believe these transformations form a useful set of basic tools for common programming tasks, we do not argue that these constitute a necessary or sufficient set. One benefit of our design is that different sets of transformationssuch as refactorings for class-based languages [Fowler 1999], refactorings for functional languages [Thompson and Li 2013], transformations that selectively change program behavior [Reichenbach et al 2009], and task-specific transformations that do not have common, recognizable names [Steimann and von Pilgrim 2012]-can be incorporated and displayed to the user within our interface.…”

Scaling Reliably

“…Refactoring [65,32,75] is the process of changing how a program works without changing what it does. This can be done for readability, for testability, to prepare it for modification or extension, or -as is the case here -in order to improve its scalability.…”