Effective Haskell: Calculator throws errors in parse'

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Hi, it looks like you’re missing the lit parameter to readEither in the parse' function. The correct version of the function is:

parse' :: [String] -> Either String (Expr, [String])
parse' [] = Left "unexpected end of expression"
parse' (token:rest) =
  case token of
    "+" -> parseBinary Add rest
    "*" -> parseBinary Mul rest
    "-" -> parseBinary Sub rest
    "/" -> parseBinary Div rest
    lit ->
      case readEither lit of
        Left err -> Left err
        Right lit' -> Right (Lit lit', rest)

It looks like this is fixed in the most recent version- thanks for the catch and sorry for the trouble!