[Haskell-cafe] Interaction in Haskell

Henning Thielemann lemming at henning-thielemann.de
Mon Jul 11 07:54:36 EDT 2005

On Mon, 11 Jul 2005, Dinh Tien Tuan Anh wrote:

> Hi,
> im using Hugs 98 and learing how to use interactive Haskell.
> As read in the book:
>       capitalise :: [Char] -> [Char]
>       capitalise = takeWhile(/='.') . map toUpper
>       interact capitalise
> its said the program is FULLY INTERACTIVE, i.e: as soon as 'h' typed on the
> keyboard, an 'H' appears on the screen. But the program above always waits
> untill ENTER was hit to display the result
> Is this normal ? Is the book right ?

Yes, it is certainly not Hugs which prevents from realtime interaction but
it is the terminal you are using. If the terminal lets you delete the
characters on the current line it has to keep them until you complete it
with ENTER.  Piping from and to other programs or files may not have this

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