[Haskell-cafe] Type level natural numbers

[Mateusz Kowalczyk]

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About two weeks ago we got an email (at ghc-users) mentioning that
comparing to 7.6, 7.7.x snapshot would contain (amongst other things),
type level natural numbers.

I believe the package used is at [1].

Can someone explain what use is such package in Haskell? I understand
uses in a language such as Agda where we can provide proofs about a
type and then use that to perform computations using the type system
(such as guaranteeing that concatenating two vectors together will
give a new one with the length of the two initial vectors combine)
however as far as I can tell, this is not the case in Haskell
(although I don't want to say ?impossible? and have Oleg jump me).

- -- 
Mateusz K.
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