How do you fix Parse error on input ‘->’ on Haskell?

Question

The code below is for a calculator I have written. I am trying to handle parse error and token error but I keep receiving the same error on ∖s -> tokens s How do I fix this? Why do I keep getting this error?

 {- main -}
 main = do cs <- getContents
           putStr $ unlines $ map show $
            map (∖s -> tokens s >= parse >= eval) $ lines cs

Your code is not properly indented. cs and putStr should start on exactly the same column. — chi
– chi, Commented Jan 5, 2021 at 9:01

bradrn · Accepted Answer · 2021-01-05 09:21:15Z

5

The problem here is a subtle one. The correct syntax is \s -> tokens s >= parse >= eval, using a backslash: \ U+005C REVERSE SOLIDUS. However, instead your code is ∖s -> tokens s >= parse >= eval. This is subtly different: instead of using a backslash as expected, it instead uses ∖ U+2216 SET MINUS. Simply use the correct character, by replacing ∖ with \, and it should parse correctly.

answered Jan 5, 2021 at 9:21

bradrn

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