For the style part, I recommend hlint [1]. Regarding the testing, QuickCheck is excellent and I have been happy with it so far.
>From a more general point of view, I agree with a point of view that many haskellers seem to share, but that Cale Gibbard put in words on #haskell regularly. It consists in looking at your code from a higher point of view and trying to express what you wrote in a "sublanguage" of primitives and combinators. He pointed to [2] for more details and examples. Hope it helps. [1] http://community.haskell.org/~ndm/hlint/ [2] http://contracts.scheming.org/ On Tue, Mar 2, 2010 at 8:20 PM, Sean Leather <leat...@cs.uu.nl> wrote: > There are numerous threads on the Haskell Café involving rewriting, > refactoring, refining, and in general improving code (for some definition of > improve). I am interested in seeing examples of how Haskell code can be > rewritten to make it better. Some general examples are: > > - Eta-reduce > - Make more pointfree > - Introduce monadic operators or do-notation > - e.g. for Maybe, lists, State > - Eliminate monadic operators or do-notation > - Generalize types > - e.g. change map to fmap, (++) to mappend > - Use instances of Functor, Applicative, Alternative, Category, > Arrow, Monoid, Traversable, etc. > - Use library functions from Data.List, Data.Map, Data.Set, etc. > - Use some form of generic programming (e.g. SYB, Uniplate, EMGM, > Alloy) > - Use other libraries not included in the Platform > > > My question is simple: > > *How do you rewrite your code to improve it?* > > You can answer this in any way you like, but I think the most useful answer > is to show a reasonably small, concrete example of what your code looked > like before and after. Also, please describe how you think the rewrite > improves such code. > > - Is it better style? More useful? More efficient? > - Are the types (before and after) the same? > - Are the semantics the same? > - How did you prove or test equivalence? (e.g. Can you use equational > reasoning to confirm the rewrite is valid? Did you use QuickCheck?) > > > Here is an example that I find myself doing occasionally. > > For all x, f: > > x >>= return . f > --> > fmap f x > or > f <$> x -- requires importing Control.Applicative > > I think the right-hand side (RHS) is more concise and simpler. The types > here do change: the type constructor has a Monad constraint in the left-hand > side and a Functor constraint in the RHS. Types that are Monad instances are > generally also Functor instances, so this is often possible. I'm convinced > the semantics are preserved, though I haven't proven it. > > What's an example of a rewrite that you've encountered? > > Thanks, > Sean > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > -- Alp Mestanogullari http://alpmestan.wordpress.com/ http://alp.developpez.com/
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