[Haskell-cafe] MRP, 3-year-support-window, and the non-requirement of CPP

Manuel Gómez targen at gmail.com
Wed Oct 7 22:42:09 UTC 2015

On Wed, Oct 7, 2015 at 4:43 PM, Mark Lentczner <mark.lentczner at gmail.com> wrote:
> If you don't intend to actually deprecate it.
> Why bother?
> But seriously, why do you think that "you would still be able to use it"?
> That is true for only the simplest of code - and untrue for anyone who has a
> library that defines a Monad - or anyone who has a library that they want to
> keep "up to date". Do you really want to have a library where all your "how
> to use this" code has return in the examples? Shouldn't now be pure? Do I
> now need -XCPP just for Haddock? and my wiki page? And what gets shown in
> Hackage? This is just a nightmare for a huge number of libraries, and
> especially many commonly used ones.
> Why bother!

This is explained in the original proposal.  In particular, it
eliminates opportunities for errors and simplifies ApplicativeDo.  I
don’t believe anyone has proposed removing return from base.  The only
proposed change is turning return into a stand-alone function instead
of a method in Monad.  There is no proposal for removing return.

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