[Haskell-cafe] Question, re: type class syntax.

[William Yager]

Hey David,

I think there might be a bit of confusion here. When you say "LogTree2 a",
that means "a" is an instance of "LogTree2". Maybe you want something like
this?

evaluator :: LogTree2 a => a -> SizedVector a -> SizedVector a

Some context might help us to understand what you're going for.

--Will


On Sat, Aug 29, 2015 at 7:30 PM, David Banas <capn.freako at gmail.com> wrote:

> Thanks, Will.
> Maybe I’ve got the syntax all wrong, but my intent is just to constrain
> the type ’t’ to be of class 'LogTree2 a’.
> -db
>
> On Aug 29, 2015, at 5:27 PM, William Yager <will.yager at gmail.com> wrote:
>
> If you want the "LogTree2" typeclass to have multiple type arguments
> (which it looks like you do, from the definition of "evaluator"), you need
> to define it as
>
> class (Show a, Num a) => LogTree2 a t where
>
> --Will
>
> On Sat, Aug 29, 2015 at 6:45 PM, David Banas <capn.freako at gmail.com>
> wrote:
>
>> Hi all,
>>
>> I can’t figure out why this is invalid:
>>
>> class (Show a, Num a) => LogTree2 a where
>>     evaluator :: (LogTree2 a) t => t -> SizedVector a -> SizedVector a
>>
>> error| ‘LogTree2’ is applied to too many type arguments In the type
>> ‘(LogTree2 a) t => t -> SizedVector a -> SizedVector a’ In the class
>> declaration for ‘LogTree2’
>>
>> Can anyone help me understand?
>>
>> Thanks,
>> -db
>>
>>
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>>
>
>
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