# racket-bitsyntax

Adds library support for slices and splices of byte-vectors to Racket,
and adds syntax for pattern-matching such bit-strings, inspired by
Erlang's binary pattern-matching:

 - <http://www.erlang.org/doc/reference_manual/expressions.html#id77409>
 - <http://www.erlang.org/doc/programming_examples/bit_syntax.html>

Here's a Racket equivalent of the example given in the Erlang documentation:

    (bit-string-case datagram
      [( (= IP-VERSION :bits 4)
         (? header-length :bits 4)
         (? service-type)
         (? total-length :bits 16)
         (? id :bits 16)
         (? flags :bits 3)
         (? fragment-offset :bits 13)
         (? ttl)
         (? protocol)
         (? header-checksum :bits 16)
         (? source-ip :bits 32)
         (? destination-ip :bits 32)
         (? rest :binary) )
       (when (and (>= header-length 5)
                  (>= (bit-string-length datagram) (* header-length 4))))
       (let ((options-length (* 4 (- header-length IP-MINIMUM-HEADER-LENGTH))))
         (bit-string-case rest
           [( (? opts :binary :bytes options-length)
              (? data :binary) )
            'datagram-valid]))]
      [else
       'datagram-not-valid])