On Fri, 2010-10-08 at 01:13 +0300, Lauri Alanko wrote: > Your "general" rule doesn't subsume your case example, since a case > expression is not an application. I think you mean something like > > do C[(<- m)] > => > m >>= \tmp -> C[tmp] > > where C is an arbitrary expression context. It could further be > generalized to allow several (<- ...) subterms in an expression, with > implied left-to right sequencing.
Yes, that's what I meant. Thanks for describing it properly. On Fri, 2010-10-08 at 05:41 -0700, Nicolas Pouillard wrote: > Imagine find this code: > > do s1 > C[(<- s2)] > > And I don't see the (<- s2) in C, and so I refactor it as: > > s1 >> C[(<- s2)] This is roughly what I meant with "abused": Where "C" is very complex, it might become non-obvious where exactly the monad actions are supposed to happen. Hence such traps when refactoring. Also of note: Just moving sub-expressions around isn't something that is guaranteed to be save. Introducing new names and using them in "s2" would be problematic, for example: do map (\x -> (<- putStrLn x)) ["a", "b"] Obviously can't be made to work. You might have to check for this - or maybe even disallow the shorthand inside lamdbas and lets. Might be less satisfying to have such special cases, but it is still a good bit more general than what is available right now. Greetings, Peter Wortmann _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
