Re: [Haskell-beginners] how can I make this work

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 wrote:

Thanks,

Now I see the last error on the main line :

src/Main.hs@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 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@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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