Re: [Haskell-cafe] Can't figure out cmap in hmatrix

On 05/30/2011 10:33 PM, Carter Schonwald wrote:

this is actually a bug in the type of cmap, a fix is due in the next release (at least thats what Alberto indicated to me when I asked about this a monthish ago) (note how you have the container type c e, but we want c a and c b ). Instead use the vector map or matrix map ops directly

cheers -Carter schonwald

I have just uploaded to Hackage the bug-fixed version. Thanks, Alberto

On Mon, May 30, 2011 at 3:27 PM, Mats Klingberg mailto:maklingberg@gmail.com> wrote:

Hello,

I'm playing around a bit with the hmatrix package (http://hackage.haskell.org/package/hmatrix) but can't quite figure out how to make the cmap function in Numeric.Container work.

An example:

ghci> import Numeric.LinearAlgebra ghci> let v = fromList [1.0,2.0,3.0] ghci> v fromList [1.0,2.0,3.0] :: Data.Vector.Storable.Vector ghci> :t v v :: Vector Double ghci> cmap sqrt v

<interactive>:1:1: No instance for (Container Vector e0) arising from a use of `cmap' Possible fix: add an instance declaration for (Container Vector e0) In the expression: cmap sqrt v In an equation for `it': it = cmap sqrt v

ghci> :t cmap cmap :: (Container c e, Element b, Element a) => (a -> b) -> c a -> c b

There is an instance for (Container Vector Double) but I assume that since the signature of cmap doesn't mention the type variable 'e' GHCi can't infer it. Googling hasn't helped me so far, except for digging up another post to this list with the same (?) problem, but no answer: http://www.haskell.org/pipermail/haskell-cafe/2011-April/091390.html

Is there a way to tell GHC what instance to use, or how should cmap be used?

Thanks! Mats

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