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

Murilo Winter murilo.winter at gmail.com
Thu Dec 3 22:16:07 UTC 2015


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").

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/haskell-cafe/attachments/20151203/4f13d54f/attachment.html>

More information about the Haskell-Cafe mailing list