Re: [Haskell-cafe] Re: Lambda-case / lambda-if

On Fri, 8 Oct 2010 01:13:20 +0300, Lauri Alanko wrote:

On Thu, Oct 07, 2010 at 02:45:58PM -0700, Nicolas Pouillard wrote:

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On Thu, 07 Oct 2010 18:03:48 +0100, Peter Wortmann wrote:

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Might be off-topic here, but I have wondered for a while why Haskell doesn't support something like follows:

do case (<- m) of ...

With the more general rule being:

do ... e (<- m) g => ... m >>= \tmp -> e tmp g

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. Frankly, that seems like a very attractive way to make the do-notation into a more practical imperative sub-language.

This is clearer. However this does not seems very robust against manual refactoring of the "do" notation. 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)] And so the s2 get affected somewhere else. -- Nicolas Pouillard http://nicolaspouillard.fr