[Haskell-beginners] Strange difference in behaviour between ghc and ghci

[Henry Lockyer]

A very quick reply and without reading carefully considering what may be different in GHCI  (!), 
but the output buffer flushes (at least on my system) with newline  (if you don;t flush it 'manually').
I suspect if you use putStrLn for 'what's your name' you may get something more like what you want.


On 7 Jun 2012, at 12:22, 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
> *Main> 
> 
> 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
> Matt
> 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?
> 
> Regards,
> 
> Matt.
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