Main.hs

module Main where

main :: IO ()
main = do
  str <- getLine
  let x = show (read str)
  putStrLn x

{-
$ ghc -Wall -o foo Main.hs
[1 of 1] Compiling Main             ( Main.hs, Main.o )

Main.hs:6:11: error:
    • Ambiguous type variable ‘a0’ arising from a use of ‘show’
      prevents the constraint ‘(Show a0)’ from being solved.
      Probable fix: use a type annotation to specify what ‘a0’ should be.
      These potential instances exist:
        instance Show Ordering -- Defined in ‘GHC.Show’
        instance Show Integer -- Defined in ‘GHC.Show’
        instance Show a => Show (Maybe a) -- Defined in ‘GHC.Show’
        ...plus 22 others
        ...plus 10 instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the expression: show (read str)
      In an equation for ‘x’: x = show (read str)
      In the expression:
        do { str <- getLine;
             let x = show (read str);
             putStrLn x }

Main.hs:6:17: error:
    • Ambiguous type variable ‘a0’ arising from a use of ‘read’
      prevents the constraint ‘(Read a0)’ from being solved.
      Probable fix: use a type annotation to specify what ‘a0’ should be.
      These potential instances exist:
        instance Read Ordering -- Defined in ‘GHC.Read’
        instance Read Integer -- Defined in ‘GHC.Read’
        instance Read a => Read (Maybe a) -- Defined in ‘GHC.Read’
        ...plus 22 others
        ...plus four instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the first argument of ‘show’, namely ‘(read str)’
      In the expression: show (read str)
      In an equation for ‘x’: x = show (read str)
-}