haskell - 输入 ',' 无法测试两个列表

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()

我不确定如何测试上述实现，我试图在这里传递两个不同的列表。

我不断收到:

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
 
 

Answer 1

有两件事不对:

1. 应用多个参数不使用，你可以忽略它。

2. 您不能在文件的顶层使用表达式(如函数应用程序)，而是可以将其放在 main 函数中，如下所示:

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