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Re: [Haskell-cafe] Invertible functions list

Subject: Re: [Haskell-cafe] Invertible functions list
From: Jonathan Fischoff
Date: Tue, 29 Dec 2009 07:45:15 -0800
Thirst will work I think. I tested a demo and the only problem I can see is the unwieldiness of the syntax, i.e

testThirst = f `Cons` (g `Cons` (h `Cons` Nil))

Maybe there is a way to sugar up the syntax to get rid of the parentheses?

On Mon, Dec 28, 2009 at 7:43 PM, Antoine Latter <[email protected]> wrote:
On Mon, Dec 28, 2009 at 10:32 PM, Jonathan Fischoff
<[email protected]> 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?

It looks like the thrist package should help you out:


You could define some sort of type Iso:

data Iso a b = Iso (a -> b) (b -> a)

And then build a Thrist and fold over it, the functions forward and
backwards can both be implemented with right-folds.

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