It could be my lack of knowledge. But during rename I was not able
to find the field names. But that could have been pure oversight on
my part. If they can be found I'm happy to have it expanded.
-- Lennart
On Feb 5, 2007, at 09:42 , Simon Peyton-Jones wrote:
I've applied all except the main patch.
I don't yet understand the difficulty. Why can't the renamer replace
C {..}
by
C {x1=x2, ...,xn=nx}
and behave *exactly* as if the latter had been written? Why this
stuff with the lookup function?
Admittedly, the typechecker might then emit a message showing code
the programmer didn't write, but we could take a bit of care to
make sure that didn't happen.
Simon
| -----Original Message-----
| From: [EMAIL PROTECTED] [mailto:cvs-ghc-
[EMAIL PROTECTED] On Behalf Of Lennart Augustsson
| Sent: 05 February 2007 00:11
| To: cvs-ghc@haskell.org
| Subject: Record wildcard
|
| 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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