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 On Mon, May 30, 2011 at 3:27 PM, Mats Klingberg <maklingb...@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 > > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >
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