This is a buffering problem. Use hSetBuffering to fix this (see Chapter 3 in YAHT -- www.isi.edu/~hdaume/htut/). Alternatively, use:
main = do putStrLn "Type Something:" ...
in which case the "Ln" part will force it to be printed. - Hal On Fri, 12 Sep 2003, Matt O'Connor wrote:
Hello all. I'm new to functional programming and Haskell, but have been programming in C and Java for a while. I've been going through the tutorials and whatnot on haskell.org. I've read from the Gentle Introduction to Haskell about IO and some of the other stuff and I have a question about it.
main = do putStr "Type Something: " str <- getLine putStrLn ("You typed: " ++ str)
When compile and run this code the "Type Something: " isn't displayed until the putStrLn. So there is no prompt. The output looks like this.
s Type Something: You typed: s
But if I change the putStr "Type Something: " to a putStrLn or put a \n at the end of the string it displays the text immediately (ie, when I want it to). Is there a good reason for this? Am I doing something wrong? Or do I need to call some kind of standard output flush? Thanks.
Oh, I'm using ghc.
Matt
-- Hal Daume III | hdaume@isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume