!import "base.tri" !Local
!import "list.tri" !Local
!import "bytes.tri" !Local

errUnexpectedEof = 1

ok = value rest : pair true (pair value rest)
err = code rest : pair false (pair code rest)

readU8 = (bytes : matchList
  (err errUnexpectedEof t)
  (h r : ok h r)
  bytes)

readBytesTaken = n bytes : bytesTake n bytes
readBytesRest = n bytes : bytesDrop n bytes
readBytesEnough? = n bytes : equal? (bytesLength (readBytesTaken n bytes)) n

readBytes = (n bytes :
  matchBool
    (ok (readBytesTaken n bytes) (readBytesRest n bytes))
    (err errUnexpectedEof bytes)
    (readBytesEnough? n bytes))