[Haskell-beginners] Strange difference in behaviour between ghc and ghci
a at unnali.com
Thu Jun 7 13:28:53 CEST 2012
See this similar mailing list question from 2006:
The short answer is that GHCi buffers differently, so you need to be more explicit about flushing.
On Thursday, 7 June 2012 at 9:22 PM, Matthew Moppett wrote:
> I have a very simple Haskell file (HelloWorld.hs) that reads like this:
> main = do
> putStr "What's your name? "
> n <- getLine
> putStrLn $ "Pleased to meet you, " ++ n
> When I load it into ghci, I get the following result, as expected:
> [1 of 1] Compiling Main ( HelloWorld.hs, interpreted )
> Ok, modules loaded: Main.
> *Main> main
> What's your name? Matt
> Pleased to meet you, Matt
> However, when I compile the same file using ghc and run it in a terminal, I get a very different result:
> matt at matt-Lenovo-G575:~/Haskell$ ghc HelloWorld.hs
> [1 of 1] Compiling Main ( HelloWorld.hs, HelloWorld.o )
> Linking HelloWorld ...
> matt at matt-Lenovo-G575:~/Haskell$ ./HelloWorld
> What's your name? Pleased to meet you, Matt
> matt at matt-Lenovo-G575:~/Haskell$
> -- in other words, the getLine action is being run before the putStr action, for some strange reason.
> Is this a bug? Can anyone enlighten me as to what might be going on?
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