On 21/02/14 18:52, Rodrigo Ribeiro wrote:

Hello to all!

I'm trying to install the sized-types package, a dependency for kansas lava:

http://hackage.haskell.org/package/sized-types

using cabal, and the following error message is returned:

Data/Sized/Sparse/Matrix.hs:61:26: Could not deduce (Eq a) arising from a use of `prune' from the context (Size m, Size n, Size m', Size n', n ~ m', Num a) bound by the type signature for mm :: (Size m, Size n, Size m', Size n', n ~ m', Num a) => Matrix (m, n) a -> Matrix (m', n') a -> Matrix (m, n') a at Data/Sized/Sparse/Matrix.hs:50:7-112

Is it a known issue? Is there some way to solve it? I'm using GHC 7.6.3 and plataform 2013.2.0.0.

Best,

Rodrigo

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You can just add the ‘Eq a’ constraint to the relevant line and it all compiles fine with 7.6.3. It might be worth-while to e-mail the authors and ask for a new release with the fix in place (and removing all the hard tabs from the code…). You can use ‘cabal unpack sized-types’ to fetch the package source, make the change and then ‘cabal install’ it from there. The relevant line becomes: mm :: (Eq a, Size m, Size n, Size m', Size n', n ~ m', Num a) => Matrix (m,n) a -> Matrix (m',n') a -> Matrix (m,n') a -- Mateusz K.