ashley:

witness 0.1 A witness is a value that witnesses some sort of constraint on some list of type variables. This library provides support for simple witnesses, that constrain a type variable to a single type, and equality witnesses, that constrain two type variables to be the same type. The library also provides classes for representatives, which are values that represent types.

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open-witness 0.1 Open witnesses (type IOWitness) are simple witnesses that can witness to any type. However, they cannot be constructed, they can only be generated in certain monads:

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Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/open-witness Source: http://code.haskell.org/open-witness/

You can find these packages for your local Arch Linux distribution, http://aur.archlinux.org/packages.php?ID=19194 http://aur.archlinux.org/packages.php?ID=19195 Come on Debian! :) -- Don