Re: [Haskell-beginners] why is this type wrong

I recommending first trying out the `last' function in ghci. Prelude> last [] *** Exception: Prelude.last: empty list Prelude> last [1,2] 2 Instead of using last [] = [] You can use last [] = error "Empty list" Where error is defined in a way such that it can take on any type. In ghci Prelude> :type error error :: [Char] -> a On 12 May 2015 at 12:09, Mike Meyer wrote:

On May 12, 2015 1:32 AM, "Roelof Wobben" 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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-- Regards Sumit Sahrawat