Bit Syntax Fundamentals

In Which We Descend Into Particular Detail

The bit syntax is where LFE’s approach to binary data transforms from “convenient” into “why doesn’t every language do this?” It’s a notation for describing binary data at arbitrary bit-level granularity, and it does something that would be remarkable if it weren’t so obviously sensible: it makes code look like the specification of the binary format you’re working with.

This is worth pausing to appreciate. In most languages, if someone hands you a protocol specification that says “the packet consists of a 3-bit flag field, followed by a 13-bit length field, followed by an 8-bit type identifier,” your next step involves a calculator, several bitwise operators, a growing sense of dread, and possibly a therapeutic discussion with a rubber duck about whether this career path was really the right choice.

In LFE, you write something very close to: (binary (flag (size 3)) (length (size 13)) (type (size 8))). The code reads like the spec. This is not an accident. This is deliberate design by people who had to implement telecommunications protocols and decided that life was too short for bit-masking gymnastics.