Wind-Driven State Machines Parse the Breeze

Hanging beneath my mobile, each windchime resonates to a different amateur radio callsign in morse code. As they sway in the breeze, I hear fragments: dit-dah-dit for ‘R’, dah-dit-dah-dit for ‘C’. But how would a computer parse these temporal patterns as they drift in and out of the wind?

Enter the finite state machine—a beautifully simple way to track where you are in a sequence. Like a chime that remembers whether it just rang high or low, an FSM maintains state and transitions based on input symbols. Perfect for parsing morse code streaming from swaying chimes.

In Elixir, we can model this with pattern matching that feels almost musical:

defmodule MorseParser do
  def parse(symbols, state \\ :idle)
  def parse(['.', '.', '.' | rest], :idle), do: parse(rest, :s_partial)
  def parse(['-', '-', '-' | rest], :s_partial), do: parse(rest, :sos_complete)
  def parse([:space | rest], :sos_complete), do: {:sos, parse(rest, :idle)}
  def parse([_ | rest], _), do: parse(rest, :idle)
  def parse([], state), do: state
end

Each pattern match captures a state transition, like tracking which note the chime just played. The wind might scatter the sequence, but the FSM patiently waits for the right combination.

Bash offers a different flavour—procedural but surprisingly elegant for simple state tracking:

parse_morse() {
  state="idle"
  for symbol in $@; do
    case "$state:$symbol" in
      "idle:dit") state="r_partial" ;;
      "r_partial:dah") state="r_partial2" ;;
      "r_partial2:dit") echo "Found R!"; state="idle" ;;
      *) state="idle" ;;
    esac
  done
}

The colon creates compound keys for our state transitions—a neat trick that keeps the logic linear. Whether swaying in Elixir’s functional breeze or Bash’s imperative wind, state machines capture the essence of sequential pattern recognition with mathematical elegance.