Proposal Summary: Add setEnv/unsetEnv to "base"

> I propose to add setEnv/unsetEnv to System.Environment, so that it is
> easier to write applications that behave the same on POSIX and Windows
> systems.

I finally prepared a patch for "base" [1].  Contrary to what I
originally assumed, getting it right on POSIX systems is much harder
than on Windows.

Here is the summary of the discussion:

As I understand it, Duncan Coutts, Gregory Collins, Edward A. Kmett and
Ben Millwood support the proposal.

Gregory Collins noted that

> you can get rid of unsetEnv if you make setEnv take a "Maybe String",
> which might be better.  Ultimately though, who cares what color the
> bike shed is painted :)

And I explained that

> on Windows, setEnv "FOO" "" will remove FOO from the environment.  I
> don't particularly like it, but as my stated goal was to provide the
> exact same behavior on all platforms and there is no way to work
> around this on Windows my implementation does the same thing.
>
> People who don't care for Windows support and want to set an
> environment variable to the empty string can still use "unix".
>
> So short answer: setEnv already supports removing.
>
> We could still remove unsetEnv from the public interface.  I have no
> fixed opinion on that, so I'm very open for suggestions.

Evan Laforge and Wren Thornton then provided valuable feedback on how to
improve the documentation, which I addressed.

There were no major concerns or rejections.

Cheers,
Simon

[1] http://hackage.haskell.org/trac/ghc/ticket/7427