Problem Statement

Obtain a valid   Y   or   N   response from the keyboard. The keyboard should be flushed, so that any outstanding key-presses are removed, preventing any existing   Y   or   N   key-press from being evaluated. The response should be obtained as soon as   Y   or   N   are pressed, and there should be no need to press an   enter   key.

Let's start with the solution:

import: console

: YorN
| c |
   System.Console flush
   doWhile: [
      System.Console receiveChar toUpper ->c
      c 'Y' <> c 'N' <> and
      ]
   c ;