How to call a haskell instance without explicit type

Question

I have a class with no explicit type a.

> class Binaer a where
> a_zu_binaer :: a -> String

And I am building an instance of that class. The function toBin requires as input an Integer.

> instance Binaer Integer where
> a_zu_binaer b = toBin b

Doing so I get the following error:

Inferred type is not general enough
*** Expression    : a_zu_binaer
*** Expected type : a -> String
*** Inferred type : Integer -> String

Is there a way to solve this problem? I can not give an explicit type for "a"

chi · Accepted Answer · 2019-11-02 11:00:43Z

9

Indentation matters.

class Binaer a where
a_zu_binaer :: a -> String

This defines a class with no methods, and a completely unrelated a_zu_binaer function. To make that into a method, indent it.

class Binaer a where
   a_zu_binaer :: a -> String

I'd recommend you write your code in a file, instead of entering it in GHCi. In GHCi, you will need to write everything on one line, or use one of the multi-line entry modes, but that's less convenient.

answered Nov 2, 2019 at 11:00

chi

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