(import srfi-4 bitstring)

(define bs (->bitstring (u8vector)))
(bitstring-append! bs (integer->bitstring-big #b100 3))
(bitstring-append! bs (integer->bitstring-big #b10 2))
(bitstring-append! bs (integer->bitstring-big #b1 1))
(bitstring-append! bs (integer->bitstring-big #b0101 4))