How to replace "let/in" construction with "where" in IO () function in Haskell?-CodePudding

I am studying Haskell and trying my first IO functions. Here a simple program that calculates the area of a rectangle, it works fine:

squareCalc :: IO ()
squareCalc = do
  putStrLn "Pease enter the lenght"
  length <- getLine
  putStrLn "Pleas enter the width"
  width <- getLine
  let square = read length * read width
   in putStrLn ("The square is "    show square)

However, when I try to replace "let/in" with "where":

squareCalc2 :: IO ()
squareCalc2 = do
  putStrLn "Pease enter the lenght"
  length <- getLine
  putStrLn "Pleas enter the width"
  width <- getLine
  putStrLn ("The square is "    show square) 
    where
       square = (read length) * (read width)

the compiler returns an error error:

Variable not in scope: width :: String

I am wondering if there ever possible to use "where" in functions like this?

CodePudding user response：

Nope, it's not possible. Annoying. The closest you can get is to make the thing in the where block be a function.

squareCalc2 = do
    ...
    putStrLn ("The square is "    show (square length width))
    where square length width = read length * read width