[Haskell-beginners] how can I make this work

[Alex Hammel]

The relevant part of that error message is this:

> The function ‘[1, 2]’ is applied to one argument, but its type
> [t0]
> has none

Which means that you're trying to call a list literal as though it were a
function (with one argument). Which probably means that you've got a ($)
out of place.


On Tue, 12 May 2015 at 11:16 Roelof Wobben <r.wobben at home.nl> wrote:

>  Thanks,
>
> Now I see the last error on the main line :
>
> src/Main.hs at 7:28-7:39
> Couldn't match expected type ‘[t1] -> [a0]’ with actual type
> [t0]
>  The function ‘[1, 2]’ is applied to one argument, but its type
> [t0]
>  has none … In the second argument of ‘($)’, namely ‘[1, 2] [3, 4]’ In
> the expression: print . plusplus' $ [1, 2] [3, 4]
>
> Roelof
>
>
>
>
> Alex Hammel schreef op 12-5-2015 om 20:11:
>
>  You're missing the parens around (x:yx) in the last clause.
>
> On Tue, 12 May 2015 at 11:02 Roelof Wobben <r.wobben at home.nl> wrote:
>
>>  Hello,
>>
>> I try to re implement ++
>>
>> So far I have this ;
>>
>> plusplus' :: [a] -> [a] -> [a]
>> plusplus' [] (xs) = xs
>> plusplus' [] [] = []
>> plusplus' (xs) [] =  xs
>> plusplus' (x:xs) yx = plusplus' xs x:yx
>>
>> main = print . plusplus' $ [1,2] [3,4]
>>
>>
>> But I still get this error message :
>>
>> src/Main.hs at 5:23-5:37
>> Couldn't match expected type
>> a
>>  with actual type
>> [a]
>>  a
>>  is a rigid type variable bound by the type signature for plusplus' ::
>> [a] -> [a] -> [a] at
>> /home/app/isolation-runner-work/projects/112825/session.207/src/src/Main.hs:1:14
>> Relevant bindings include yx :: [a] (bound at
>> /home/app/isolation-runner-work/projects/112825/session.207/src/src/Main.hs:5:18)
>> xs :: [a] (bound at
>> /home/app/isolation-runner-work/projects/112825/session.207/src/src/Main.hs:5:14)
>> x :: a (bound at
>> /home/app/isolation-runner-work/projects/112825/session.207/src/src/Main.hs:5:12)
>> plusplus' :: [a] -> [a] -> [a] (bound at
>> /home/app/isolation-runner-work/projects/112825/session.207/src/src/Main.hs:2:1)
>> …
>>
>>
>>
>>
>>
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>
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