Wrong IO actions order using putStr and getLine

by

This is because ghci disables buffering, while a program compiled with ghc has line buffering by default. You can see this by running this:

import System.IO
main = print =<< hGetBuffering stdout

In ghci you see NoBuffering while with runghc you get LineBuffering. Since the newline character doesn’t print until after the user input, the prompt doesn’t either.

Fix it by adding hFlush stdout after your prompt (or disable buffering with hSetBuffering stdout NoBuffering, but that’s probably bad).

More Related Contents:

  1. Memory footprint of Haskell data types
  2. When is memoization automatic in GHC Haskell?
  3. Small Haskell program compiled with GHC into huge binary
  4. A Haskell function of type: IO String-> String
  5. What’s so bad about Lazy I/O?
  6. Haskell read raw keyboard input
  7. Should do-notation be avoided in Haskell?
  8. Haskell: I/O and Returning From a Function
  9. What is fusion in Haskell?
  10. How to make a CAF not a CAF in Haskell?
  11. What does the `forall` keyword in Haskell/GHC do?
  12. Why is GHC complaining about non-exhaustive patterns?
  13. Converting IO Int to Int
  14. How to catch a no parse exception from the read function in Haskell?
  15. In what sense is the IO Monad pure?
  16. Is there a list of GHC extensions that are considered ‘safe’?
  17. Haskell \p -> not takeWhile
  18. Sum of two numbers with function in haskell
  19. How to group similar items in a list using Haskell?
  20. Memoization in Haskell?
  21. New state of the art in unlimited generation of Hamming sequence
  22. Haskell types frustrating a simple ‘average’ function
  23. Lifting a higher order function in Haskell
  24. Function definition by special cases in GHCi
  25. Lambda for type expressions in Haskell?
  26. Composing Monads v. Applicative Functors
  27. Monoidal Functor is Applicative but where is the Monoid typeclass in the definition of Applicative?
  28. How to return a pure value from a impure method
  29. How to convert Unicode Escape Sequence to Unicode String in Haskell
  30. How does Haskell printf work?

Leave a Comment