Proposal: System.Environment.getEnv should return Maybe

[Evan Laforge]

It's awkward and surprising how getEnv throws an exception when an env
var is not set, since it's very common for env vars to be optional,
and it's not convenient to catch exceptions in haskell (I have to look
up Control.Exception every time, and then add LANGUAGE
ScopedTypeVariables).  I wind up using 'fmap lookup k
Environment.getEnvironment' instead.

So I propose a function: lookupEnv :: String -> IO (Maybe String)

Then getEnv can be deprecated and eventually removed.  Or maybe not if
people want to argue the current getEnv is useful and deprecation
warnings would be too annoying.

Yeah, it's a trivial thing, but it's nice to sand off some of these rough edges.

Discussion: 2 weeks, March 7