(Sorry to break the thread, but mutt somehow managed to eat the message
I'm replying to...)
Arie Peterson:
> You could also use 'compositional functional references'. These are
> introduced in the paper "A Functional Programming Technique for Forms in
> Graphical User Interfaces" by Sander Evers, Peter Achten and Jan Kuper.
>
> === Introduction ===
>
> There are two things one typically wants to do when working with a
> substructure of some larger data structure: (1) extract the substructure;
> and (2) change the larger structure by acting on the substructure. A 'Ref
> cx t' encodes both of these functions (for a substructure of type 't' and
> larger structure (context) of type 'cx').
>
> > data Ref cx t
> > = Ref
> > {
> > select :: cx -> t
> > , update :: (t -> t) -> cx -> cx
> > }
...
> I've written a template haskell function to derive Refs from a data
>
> > structure definition
> (with record syntax): given
I've implemented this in Derive[1] in 12 minutes, counting the time
required to re-familiarize with the code. The patch is at [2] and has
also been darcs sent.
[1] http://www-users.cs.york.ac.uk/~ndm/derive
[2] http://members.cox.net/stefanor/derive-Ref-patch
Stefan
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