Erlang: The Amazingly Funky and the Amazingly Cool

Anyone who's ever looked at Erlang knows that the syntax is downright strange. For instance, Python uses "#" for comments, but Erlang interprets "8#7" as 7 in base 8 notation. Python uses "%" for modulo, but Erlang uses "%" for comments. Erlang uses "rem" for modulo, but "rem" is used as a comment delimiter in some other syntaxes.

However, I ran across some other cool tidbits. If M is a 16 bit binary value, you can unpack the first 3 bits into X, the next 7 bits into Y, and the last 6 bits into Z using the syntax:

<<X:3, Y:7, Z:6>> = M

Hence, you can parse an IPv4 datagram in a single pattern-matching operation (taken from "Programming Erlang: Software for a Concurrent World" p. 99):

-define(IP_VERSION, 4).
-define(IP_MIN_HDR_LEN, 5).
...
DgramSize = size(Dgram),
case Dgram of
  <<?IP_VERSION:4, HLen:4, SrvcType:8, TotLen:16,
    ID:16, Flgs:3, FragOff:13,
    TTL:8, Proto:8, HdrChkSum:16,
    SrcIP:32,
    DestIP:32, RestDgram/binary>> when HLen >= 5, 4*HLen =< DgramSize ->
        OptsLen = 4*(HLen - ?IP_MIN_HDR_LEN),
        <<Opts:OptsLen/binary,Data/binary>> = RestDgram,
        ...

That's about as cool as it gets for implementing binary protocols!