On Tue, May 12, 2015 at 9:42 AM Roelof Wobben <r.wobben@home.nl> wrote:

Mike Meyer schreef op 12-5-2015 om 8:39:
On May 12, 2015 1:32 AM, "Roelof Wobben" <r.wobben@home.nl> wrote:
>
> Hello,
>
> To practice recursion I try to make some functions of Data list myself on the recursive way.
>
> First I will try last.
>
> So I did this :
>
> -- | Main entry point to the application.
> module Main where
>
> -- | The main entry point.
> last' :: [a] -> a
> last' [] = []
> last' (x:xs) = last xs
>
>
> but now I see this error message :
>
> src/Main.hs@6:12-6:14
> Couldn't match expected type
> a
> with actual type
> [t0]
> a
> is a rigid type variable bound by the type signature for last' :: [a] -> a at /home/app/isolation-runner-work/projects/112712/session.207/src/src/Main.hs:5:10 Relevant bindings include last' :: [a] -> a (bound at /home/app/isolation-runner-work/projects/112712/session.207/src/src/Main.hs:6:1) …
>
> I my oponion I have said that the input is a array and the output a string,

Except for saying list instead of array, I'd agree with that. But when you write last' [] = [], the output is [], which does not have the expected type of strong. So the actual type is a list.

You need to return a string.
_______________________________________________
Beginners mailing list
Beginners@haskell.org
http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
Thanks,

I did change it to this :

-- | Main entry point to the application.
module Main where

-- | The main entry point.
last' :: [a] -> a

last' [x] = x

last' (x:xs) = last xs

So I have to look at another way to say if there is a empty list then there is no answer.
And when I run it i see this error message :

GHC threw an exception : Not in scope: ‘Main.main’

Roelof

Dit e-mailbericht is gecontroleerd op virussen met Avast antivirussoftware.
www.avast.com

_______________________________________________
Beginners mailing list
Beginners@haskell.org
http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners