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2 points by rocketnia 2774 days ago | link | parent

Scheme's 'char-ready? is probably close to what you're looking for. It returns #f if the runtime can guarantee that the stream would have blocked if it were read from at that time, and otherwise it returns #t.

  ; This exploits an Arc 3.1 bug to drop to Racket (as seen at
  ; It's unnecessary on Anarki.
  (mac $ (racket-expr)
    `(cdr `(nil . ,,racket-expr)))
  (def discard-input ((o str (stdin)))
    " Reads all the characters from the stream, giving up partway if it
      can determine the stream would block. The return value is `nil'. "
    (while:and $.char-ready?.str readc.str))
    (do (pr "enter something> ")
        (prn "The first character was " (tostring:write:readc) ".")
  enter something> something
  The first character was #\s.