Haskell使用类型为的实例读入main

如何在我的main中使用实例读取

现在我有以下几点：

data Term = Monom (Float,Int)
      | Addition (Term,Term)
      | Subtraction (Term,Term)
      | Multiplication (Term,Term)
      | Division (Term,Term)
      deriving(Show)


instance Read Term where
  readsPrec _ inp = let[(a,b)] = lex inp in
   case a of
   "x" -> readsPrec 0 b
   "^" -> [(Monom (1.0,(read b::Int)), "")]
   c  -> let[(d, "")] = readsPrec 0 b in
     [(Monom( (read c::Float),((\(Monom(x,y)) -> y) d)), "")]


--Aufruf: (read "2x^2")::Term


main :: IO ()
main = do
   putStrLn "Insert a Term:"
   inpStr <- getLine
   let outStr = (read inpStr)
   putStrLn outStr    

而不是putStrLn，因为读工具显示，但解释器让我发疯。。。

---

任何帮助都将受到欢迎

您可以在

let

中使用类型限定符。您的

main

如下所示：

main :: IO ()
main = do
   putStrLn "Insert a Term:"
   inpStr <- getLine
   let outStr = read inpStr :: Term
   putStrLn $ show outStr 

main:：IO（）
main=do
putStrLn“插入一个术语：”
inpStr
main :: IO ()
main = do
   putStrLn "Insert a Term:"
   inpStr <- getLine
   let outStr = read inpStr :: Term
   putStrLn $ show outStr