[Haskell-cafe] Invertible functions list

[Ryan Ingram]

Do you need to be able to extract the intermediate types?

If not, then the only observable value for your function list is the
composition (forward/backward), and you can easily represent it like
this:

data Inv a b = Inv { forward :: (a -> b), backward :: (b -> a) }

nil :: Inv a a
nll = Inv id id

cat :: Inv a b -> Inv b c -> Inv a c
cat ab bc = Inv (forward bc . forward ab) (backward ab . backward bc)

reverse :: Inv a b -> Inv b a
reverse ab = Inv (backward ab) (forward ab)

  -- ryan

On Mon, Dec 28, 2009 at 8:32 PM, Jonathan Fischoff
<jonathangfischoff at gmail.com> wrote:
> Hi,
> I would to create a list of tuples (or something similar) of invertible
> functions
> [((a -> b), (b -> a)), ((b -> c), (c -> b)), ....
> Such that I could call
> forward invertibleFuctionList domainValue = ? -- composite all the functions
> backward invertibleFuctionList rangeValue =
>     forward (reverse invertibleFuctionList) rangeValue  -- or something
> similar
>
> I would also like to concat them. This sounds like a job for GADT that
> someone might have already tackled. Any ideas?
> -Jonathan
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
>