[Haskell-cafe] Errors in non-monadic code

jabolopes at google.com jabolopes at google.com
Mon Aug 19 19:48:08 CEST 2013


What is the proper way to implement a non-monadic function that checks
whether a given value is correct and gives a proper error message
otherwise ? What is the recommended option ?

* Either String a

check val
  | valid val = Right val
  | otherwise = Left errorMsg

* Maybe String

check val
  | valid val = Nothing
  | otherwise = Just errorMsg


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