Proposal: Add IsString and Monoid instances for Doc

[Bas van Dijk]

Hello,

Since we're discussing a proposal for the pretty package I would like
to make another one:

The proposal is to add the following to Text.PrettyPrint.HughesPJ:

instance IsString Doc where
    fromString = text

This allows users to use string literals as Doc values using the
OverloadedStrings language extension.

I would also like to add:

instance Monoid Doc where
    mempty  = empty
    mappend = (<>)

If there's enough demand (because it's a lot of work) I can find out
if this change breaks anything by analyzing pretty's direct reverse
dependencies:

http://bifunctor.homelinux.net/~roel/cgi-bin/hackage-scripts/revdeps/pretty-1.0.1.1#direct

to see if some of them define an orphaned instance for IsString or Monoid.

The patch that implements this is attached to the ticket:

http://hackage.haskell.org/trac/ghc/ticket/4378

Deadline: 2 weeks (Friday 22 October 2010)

Regards,

Bas