Re: [Haskell-cafe] Strange error with type classes + associated types

On Sun, Apr 18, 2010 at 9:02 PM, Brent Yorgey wrote:

Conal,

Thanks for looking into this! Making (:-*) into a proper type seems promising. I did try wrapping (:-*) in a newtype but that didn't help (although I didn't expect it to).

What do you mean by a "proper type"? I didn't know what Roman meant either, though I guessed he meant a newtype or data type.

I see you just uploaded a new version of vector-space; what's new in 0.6.2?

The dependency on the Boolean package now specifies >= 0.0.1.

-Brent

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Oh! I'd completely forgotten about this idea. Looking at Data.LinearMap in vector-space, I see a comment about exactly this ambiguity, as well as

On Sat, Apr 17, 2010 at 10:28:45AM -0700, Conal Elliott wrote: the

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start of a new module that wraps a data type around the linear map representation. I don't recall whether I got stuck or just distracted.

On Sat, Apr 17, 2010 at 3:46 AM, Roman Leshchinskiy

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On 17/04/2010, at 11:00, Conal Elliott wrote:

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I'm unsure now, but I think I tried making Basis a data type (not syn) and ran into the problem I mentioned above. The Basis *synonyms* also have HasTrie instances, which is crucially important. If we switch to (injective) data types, then we lose the HasTrie instances. I'd be okay with defining HasTrie instances (preferably via "deriving") for the associated Basis data types, but I couldn't figure out how to. Maybe it's not possible currently, or maybe I just didn't know how.

Could you perhaps make (:-*) a proper type rather than a synonym? That would help with the ambiguity.

Roman

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