The Fundamental Symmetry

One of the more elegant properties of LFE’s binary syntax is its perfect symmetry: the same syntax used to construct a binary can be used to deconstruct it through pattern matching. This is rather like how a proper towel can both dry you off and serve as a makeshift sail, blanket, or weapon, depending on which end you grab.

Construction vs. Deconstruction

; Construction: Building a binary
lfe> (set data (binary ((42 (size 8)) (314159 (size 32)))))
#B(42 0 4 203 47)

; Deconstruction: Pattern matching to extract values
lfe> (binary ((answer (size 8)) (pi-ish (size 32))) data)
#B(42 0 4 203 47)
lfe> answer
42
lfe> pi-ish
314159

The pattern (binary ((answer (size 8)) (pi-ish (size 32))) data) says: “Take the binary in data, extract 8 bits into answer, then extract 32 bits into pi-ish.” The pattern matching will either succeed (binding the variables) or fail (crashing with appropriate alarm), much like attempting to teleport through a device that might not be entirely reliable.