getbyte char unit(163)
[
  char nb
  int signal
  nb=unit(35)
  if(nb<=0)[
    signal=fread(unit+36,unit)
    if(signal== -1)return 26 /* ^Z returned.
    if(signal< -1)[
      ps"read error"; return 26
    ]
    nb=0
  ]
  unit(35)=nb+1
  return unit(nb+36)
]
putbyte char c,unit(163)
[
  char nb
  int signal
  nb=unit(35)
  if(nb<0)[
    signal=fwrite(unit+36, unit+163, unit)
    nb=0
  ]
  unit(36+nb)=c
  if(c==26) if(nb>0)[
    signal=fwrite(unit+36, unit+163, unit)
    nb=0
  ]
  unit(35)=nb+1
  return signal
]