Function whitec needs this, as part of arc.arc, and it's not provided by ArcJS. ArcJS can't escape #\space or #\newline defined by Racket.

From http://smihica.github.io/arc-js/

  ;; ArcJS 0.1.2
  arc> (def whitec (c)
         (in c #\space #\newline #\tab #\return))
  ;; passed -- read:0ms compile:111ms eval:1ms total:112ms
  #<fn:whitec>
  arc> (prn (whitec ("test" 0)))
  ;; passed -- read:0ms compile:4ms eval:0ms total:4ms
  Error: Unbound variable pace
  Stack Trace:
  _______________________________________
    0  fn 'whitec'
          EXECUTED (whitec #\t #\s)