Thanks
Can I just say Main =
I will google to look how to make a safeLast.
Roelof
Alexey Shmalko schreef op 12-5-2015 om 8:46:
last' [] = error "last' on empty list"
Otherwise, you should wrap the result in Maybe to make your function work as safeLast.
Oh... GHC's exception seems to say you haven't defined `main` in your module.
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.
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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’
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