Input ',' cannot test two lists

Question

inter :: [Integer] -> [Integer] -> [Integer]
inter s1 s2 = [s | s <- s2, s `elem` s1]

inter [5, 6, 3, 1], [5, 2, 1, 3]

main = return()

I am not sure of how to test the above implementation, I am trying to pass two different lists here.

I keep getting:

GHCi, version 8.10.6: https://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /home/runner/University-Labs/.ghci
[1 of 1] Compiling Main             ( Main.hs, interpreted )

Main.hs:4:19: error: parse error on input ‘,’
  |
4 | inter [5, 6, 3, 1], [5, 2, 1, 3]
  |                   ^
Failed, no modules loaded.
 
<interactive>:1:1: error:
    • Variable not in scope: main
    • Perhaps you meant ‘min’ (imported from Prelude)
 ^C Leaving GHCi.
repl process died unexpectedly: 
GHCi, version 8.10.6: https://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /home/runner/University-Labs/.ghci
 


Noughtmare · Accepted Answer · 2022-09-20 12:54:04Z

8

There's two things wrong:

Applying multiple arguments does not use , you can just leave that out.
You cannot use expressions (like function application) at the top-level in a file, instead you can put it in the main function as follows:

inter :: [Integer] -> [Integer] -> [Integer]
inter s1 s2 = [s | s <- s2, s `elem` s1]

main = do
  print (inter [5, 6, 3, 1] [5, 2, 1, 3])
  -- you can do more here if you want

answered Sep 20, 2022 at 12:54

Noughtmare

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