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

Mark Lentczner mark.lentczner at gmail.com
Wed Oct 7 21:13:02 UTC 2015

On Wed, Oct 7, 2015 at 9:38 AM, Erik Hesselink <hesselink at gmail.com> wrote:

> While I don't think it detracts from your argument, it seems you
> misread the original proposal. At no point will it remove `return`
> completely. It would be moved out of the `Monad` class and be made
> into a top-level definition instead, so you would still be able to use
> it.

Then why bother?
If you don't intend to regard code that uses "return" as old, out-dated, in
need of updating, etc....
If you don't intend to correct people on #haskell to use pure instead of
If you don't tsk tsk all mentions of it in books....
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!
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