Only really used in parsing config files derived from command line flags.

It is ghc's optimised InstalledPackageInfo parser that needs updating.

rolling back:

Fri Dec 12 18:36:22 GMT 2008  Ian Lynagh <igloo@earth.li>
  * Fix Show/Read for License
  We were ending up with things like
      InstalledPackageInfo {
          ...
          license = LGPL Nothing,
          ...
      }
  i.e. "LGPL Nothing" rather than "LGPL", which we couldn't then read.

    M ./Distribution/License.hs -2 +14

Put the more important one first.

extend it rather than overriding it.
Also rearrange slightly the default global --help output.

I dunno, some people...

We support using multiple package dbs, however the method for
specifying them is very limited. We specify a single package db
and that implicitly specifies any other needed dbs. For example
the user or a specific db require the global db too. We now
represent that stack explicitly. The user interface still uses
the single value method and we convert internally.

We were ending up with things like
    InstalledPackageInfo {
        ...
        license = LGPL Nothing,
        ...
    }
i.e. "LGPL Nothing" rather than "LGPL", which we couldn't then read.

Distribution/Simple/PreProcess.hs uses it, so this causes build failures
with -Werror.

Rather than two, and do it in a simpler way.

This eliminates the duplicate representation of ">= 0" vs "-any"
and makes VersionIntervals properly canonical.

One property fails. The failure reveals that the VersionInterval type
is not quite a canonical representation of the VersionRange semantics.
This is because the lowest Version is [0] and not -infinity, so for
example the intervals (.., 0] and [0,0] are equivalent.

With properties.

Version numbers have to be a non-empty sequence of non-negataive ints.

This fixes a bug in cabal-install

Also document the functions in the ModuleName module.

and check internal invariants

Implement it in terms of the -XRecordPuns which was accidentally
added in ghc-6.8 and deprecates in 6.10 in favor of NamedFieldPuns
So this is for compatability so we can tell package authors always
to use NamedFieldPuns instead.

Along with possibly another extension that replaces it.

Check for new language extensions added in Cabal-1.2 and also 1.6.
Simplify the checking of -X ghc flags. Now always suggest using
the extensions field, as we separately warn about new extenssons.

Provide asVersionIntervals as the view function for a VersionRange
This will let us enforce the internal data invariant

Previously if one or the other or both were missing we only warned.
Now if neither are given it's an error. We still warn about either
missing.

For Functor, Monoid and Traversable.