Record wildcard

[Lennart Augustsson]

Here's the complete record wildcard patch.
Even if you don't accept the (somewhat ugly) patch to implement the  
wildcarding it
would be nice if you could apply all the minor ones (i.e., all but  
the last).

	-- Lennart

Implement C{..} notation for expressions and patterns.

The C{..} notation is used as a short hand for C{x1=x1, x2=x2, ...}
where xn are all the fields of the constructor C.
This features is activated by using the -frecord-wildcard flag.
For example, the following is valid:
data C = C { x :: Int, y :: Int }
f a =
      let x = 1
          y = x + a
      in  C{..}
g C{..} = x + y
The C{..} in a pattern is a little dubious since it introduces bound  
variables
with no obvious binding site.  But it is extremely handy for  
accessing records
with a large number of components.  (The construct has a long  
tradition with
names like open/with/use.)
The implementation for C{..} in expressions is reasonable clean.  But  
the
implementation for patterns really needs fixing.  It only barely works
because it is able to hijack the globally bound field selector names.
It also interacts very badly with any feature that uses  
collectPatBinders
since this function does not return the correct set when C{..} is used.

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