[Haskell-cafe] Creating an instance of the Show Typeclass for a datatype

[NCrashed .]

Hi,

instance Show Stat where
  show (a, b) = "the value of " ++ a ++ " is " ++ show b

I pretty sure you need also enable TypeSynonymInstances extension. One way
to do it is to add "{-# LANGUAGE TypeSynonymInstances #-}" just at the
beginning of your module.

Best wishes

2015-12-04 1:16 GMT+03:00 Murilo Winter <murilo.winter at gmail.com>:

> Hello,
>
> As part of my exercise, I have to create an instance of the show typeclass
> for a given data type defined as:
>
>    1. *type *stat *= (*String*, Int)*
>
> *If* it was a data type, like:
>
>    1. data TrafficLight = Red | Yellow | Green
>
>
> It would be as simple as doing:
>
>    1. instance Show TrafficLight where
>    2.     show Red = "Red light"
>    3.     show Yellow = "Yellow light"
>    4.     show Green = "Green light"
>
>
> However, I do not know how to declare the instance for a type, and then
> how to access its elements (String and Int).
>
> This is what I have so far, which does not work:
>
>    1. instance Show Stat where
>    2.     show stat(a,b) = a
>
> instance Show Stat where
>   show stat(a b) = b
>
> (imagine, for example, I desire to write" the value of "String" is "Int").
>
> Thanks,
>
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