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

[Alberto Ruiz]

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 <maklingberg at gmail.com
> <mailto:maklingberg at 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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