[Haskell-cafe] Newbie list question

[Andrew Coppin]

junkywunky wrote:
> type Person = (NI, Age, Balance)
> type Bank = [Person]
>
> credit :: Bank -> [Person]
> credit [(a,b,c)] = [(a,b,c)]
>
> This code works when I type in:
>
> credit [(1,2,3)]
>
> but doesn't work when I type in:
>
> credit [(1,2,3),(4,5,6)]
>
> Any help?
>
> Thanks in advance.
>   

The expression [(1,2,3),(4,5,6)] doesn't match the pattern [(a,b,c)].

Now, since Bank and [Person] are actually the exact same type and the 
credit function actually does nothing, you could simply write

  credit x = x

(Or, for that matter, credit = id.) It would then work for both examples.

I presume that the idea is that the credit function will eventually do 
something - in that case, it might be helpful to say exactly what you 
want it to actually do.