[Haskell-beginners] type vs data, again...

Emmanuel Touzery etouzery at gmail.com
Sun Mar 17 16:16:41 CET 2013

Thank you, that was the trick! It would be handy it there was a way through
the online hackage packages pages to click through the dependencies. I
guess you checked the .cabal by hand or used some slightly more arcane
cabal commands to get that information.

Thank you again and nice rest of week-end!


On Sun, Mar 17, 2013 at 2:51 PM, Andres Löh <andres at well-typed.com> wrote:

> Hi again.
> >  thank you for the tip! It helps but it's not quite there yet. If you see
> > the program in attachment, I can make it compile only by commenting the
> type
> > declaration for the second function, otherwise it's the exact same error
> > message as before.
> You're probably using the wrong HashMap. There are several packages on
> Hackage implementing similarly-named data structures (which is
> confusing, I know, but such is life in a decentralized and open
> world). You should use what aeson is using (because that's the library
> defining the Object type synonym).
> Looking at the import list of
> http://hackage.haskell.org/packages/archive/aeson/
> we see
> import Data.HashMap.Strict (HashMap)
> and by checking the package dependencies of aeson, we figure out that
> this module is provided by the unordered-containers package.
> Cheers,
>   Andres
> --
> Andres Löh, Haskell Consultant
> Well-Typed LLP, http://www.well-typed.com
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