Thank you, that was exactly what I needed. Now program compiles flawlessly.
2010/11/10 Neil Brown <nc...@kent.ac.uk>: > Hi, > > You have a problem with your function getPhi. It has type: > > getPhi :: forall a e m. (MutableMatrix a e m, Typeable a, Typeable e, > Floating e, Ord e) => VarStateT m () > > where MutableMatrix is: > > class (PrimMonad m) => MutableMatrix a e m | a -> e m where > > No matter how you call getPhi, you can't specify the 'a' and 'e' types -- > they don't appear in the real part of the type signature, and the fundep on > the MutableMatrix class is not sufficient to determine 'a' or 'e' from 'm'. > This means that there is no way for the compiler to pick a type for 'a' or > 'e' when getPhi is called, and there is no way to make the 'a' and 'e' for > getPhi be the same as the 'a' and 'e' for compute. getPhi needs to know > what type it is attempting to cast the dynamic state into and at the moment > you can't tell it. > > The solutions that I can think of are either to pass dummy parameters of > type 'a' and 'e' to allow you to specify the type, or to add a fundep like m > -> a e (but I don't think that one holds?). > > Thanks, > > Neil. > > On 10/11/10 13:10, Vladimir Matveev wrote: >> >> Hi, >> I want to use something like (Control.Monad.StateT (Data.Map.Map >> String Dynamic) m). So I wrote VarStateT datatype and corresponding >> classes (Control/Monad/VarState.hs in [1]). Then I tried to use it in >> my program (Math/Eigenvalues.hs in [1]). But compiler refused to >> compile it with many type errors. I thought that it would be >> sufficient to use ScopedTypeVariables and write all type annotations. >> It helped slightly, many messages were gone, but now compiler throws >> an error I don't know how to solve. >> >> ghc --make -o out/eigenvalues -outputdir build Main.hs >> [3 of 4] Compiling Math.Eigenvalues ( Math/Eigenvalues.hs, >> build/Math/Eigenvalues.o ) >> >> Math/Eigenvalues.hs:14:30: >> Could not deduce (MutableMatrix a e m) >> from the context (MutableMatrix a2 e2 m, >> Typeable a2, >> Typeable e2, >> Floating e2, >> Ord e2) >> arising from a use of `getPhi' at Math/Eigenvalues.hs:14:30-35 >> Possible fix: >> add (MutableMatrix a e m) to the context of >> the type signature for `compute' >> In the second argument of `(>>)', namely `getPhi' >> In the first argument of `(>>)', namely `maxElem a>> getPhi' >> In the first argument of `(>>)', namely >> `maxElem a>> getPhi>> buildB' >> >> Math/Eigenvalues.hs:14:40: >> Could not deduce (MutableMatrix a1 e1 m) >> from the context (MutableMatrix a2 e2 m, >> Typeable a2, >> Typeable e2, >> Floating e2, >> Ord e2) >> arising from a use of `buildB' at Math/Eigenvalues.hs:14:40-45 >> Possible fix: >> add (MutableMatrix a1 e1 m) to the context of >> the type signature for `compute' >> In the second argument of `(>>)', namely `buildB' >> In the first argument of `(>>)', namely >> `maxElem a>> getPhi>> buildB' >> In the first argument of `(>>=)', namely >> `maxElem a>> getPhi>> buildB>> buildA' >> >> How to sort this out? >> >> [1] http://dl.dropbox.com/u/1415321/prog/eigenvalues.tar.gz >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe@haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
