[Haskell-cafe] Contravariant applicatives, monads and arrows (was ANN: rematch, an library for composable assertions with human readable failure messages)

Stephen Tetley stephen.tetley at gmail.com
Tue Apr 16 20:48:47 CEST 2013

On 16 April 2013 16:12, Alejandro Serrano Mena <trupill at gmail.com> wrote:
> Hi,
> First of all, let me say that this work on matchers is really useful :)
> Following Roman advice, I'm trying to find a more principled approach
> that could be useful for this library. It seems that "Match" could
> easily be converted to Either and thus made into Functor, Applicative,
> Alternative and Monad. That would allow to write things like:

Have you seen Ralf Hinze, Johan Jeuring and Andreas Loeh's  paper on Contracts?

The found their Contract datatype formed a comonad - at the time this
seemed to be one of the few (non-synthetic) uses of comonads.

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