Pardon My Parsing...

Advent of Code 2016 problems

Since they all involve parsing some kind of input data, this will be a job for ... Instaparse!
With it we can use a context-free grammar to generate a tree-like structure from our data.
For example, here an input string for the day 4 problem. Each room is represented as a key, id and checksum:

aaaaa-bbb-z-y-x-123[abxyz]

The key is made of one or more strings of letters separated with hyphens. The id is a string of numbers, and the checksum is a string of letters in brackets. This is how we represent that in EBNF notation... In Clojure!:

(def room-parser
  (insta/parser
    "room = key id checksum
    key = (word <separator>)+
    <separator> = '-'
    word = #'[a-zA-Z]+'
    checksum = <'['> word <']'>
    id = #'[0-9]+'"))

Now we pass the input to our shiny-new parser:

(room-parser "aaaaa-bbb-z-y-x-123[abxyz]")

And we get our magical tree! Ooowee!

=> [:room [:key [:word "aaaaa"] [:word "bbb"] [:word "z"] [:word "y"] [:word "x"]]
[:id "123"]
[:checksum [:word "abxyz"]]]

We can even make a pretty little chart using rhizome and graphviz! Oooweee!

(insta/visualize  (room-parser "aaaaa-bbb-z-y-x-123[abxyz]"))

Let's do another one!
Day 10 we are programming robots.
The input data consists of instructions like this:

bot 147 gives low to bot 67 and high to bot 71
bot 142 gives low to bot 128 and high to bot 164
bot 47 gives low to bot 4 and high to bot 209
bot 107 gives low to bot 194 and high to bot 103
bot 102 gives low to bot 82 and high to bot 3
bot 101 gives low to bot 46 and high to bot 111
value 23 goes to bot 76

We'll break it down to the first line:

(def bots "bot 147 gives low to bot 67 and high to bot 71")

Now we'll express the relevant data in EBNF notation:

(def bot-parser
  (insta/parser
    "handoff = bot+
     bot = word whitespace id
     word = #'[a-zA-Z]+'
     whitespace = #'\\s+'
     id = #'[0-9]+'"))

Each transaction performed by the bots is represented as a "handoff". A handoff can involve any number of bots, a transmitter followed by one or more receivers.
Let's use this parser to visualize this transaction:

(insta/visualize (bot-parser bots))