Question

I had a datatype, example:

data MyData = Something1 String

and then I had a function

myFunction :: MyData -> String
myFunction x = x

within myFunction I want to refer to the characters ie [‘S’,’o’,’m’,’e’……’1′] which are in my data type MyData. However, I get the following error:

Couldn’t match expected type [Char]'
with actual typeMyData’
Expected type: String
Actual type: MyData

As far as I understand [Char] is the same as String, and I have declared ‘Something1’ as String, so it should work?

Answer 1

[Char] is the same as String, but neither is the same as MyData. To access the string stored within your data type, you’ll need to use pattern matching:

myFunction :: MyData -> String
myFunction (Something1 xs) = xs

This is because the data keyword makes a completely new data type. If you only wanted an alias, you could also use the type keyword:

type MyData = String

myFunction :: MyData -> String
myFunction x = x