Reading characters from input

[David Skoupil <skoupil@alpha.inf.upol.cz>]

Hi everyone, 

I am looking for a quick (and easy) way of reading characters from
keyboard without waiting for "Return" key, possibly including special
characters like keyboard arrows.

(I'm using Scheme for teaching high school students the basics of
comp. programming this summer and I would like to use the keyboard to
navigate turtle in the turtle geometry package.)
 
Thanks for any help. 

David Skoupil