Day 2

lib/common.ex

@@ -1,4 +1,15 @@
 defmodule Aoc2023.Common do
   def stringify(s) when is_binary(s) do s end
   def stringify(n) when is_integer(n) do inspect(n) end
+  def stringify(nil), do: "nil"
+
+  def map_nth(tup, n, fun) do
+    put_elem(tup, n, fun.(elem(tup, n)))
+  end
+
+  defmacro pipe(expr) do
+    quote do
+      fn (val) -> val |> unquote(expr) end
+    end
+  end
 end

lib/day2.ex

@@ -0,0 +1,52 @@
+defmodule Aoc2023.Day2 do
+  use Aoc2023
+
+  def parse(input) do
+    input
+    |> String.split("\n")
+    |> Enum.map(pipe(
+        String.split(": ")
+        |> then(fn ["Game " <> id, rounds] ->
+          {String.to_integer(id),
+           rounds
+           |> String.split("; ")
+           |> Enum.map(pipe(
+               String.split(", ")
+               |> Enum.map(pipe(
+                   String.split(" ")
+                   |> then(fn [n, color] ->
+                     {String.to_existing_atom(color), String.to_integer(n)}
+                   end)
+               ))
+           ))}
+        end)
+    ))
+    |> Enum.into(%{})
+  end
+
+  @part1_available [
+    red: 12, green: 13, blue: 14
+  ]
+  def part1(input) do
+    input
+    |> Enum.filter(pipe(
+      elem(1)
+      |> Enum.all?(pipe(
+         Enum.all?(fn {color, num} -> Keyword.get(@part1_available, color, 0) >= num end)
+      ))
+    ))
+    |> Enum.map(pipe(elem(0)))
+    |> Enum.sum
+  end
+
+  def part2(input) do
+    input
+    |> Enum.map(pipe(
+      elem(1)
+      |> Enum.reduce(&(Keyword.merge(&1, &2, fn _, m1, m2 -> max(m1, m2) end)))
+      |> Enum.map(pipe(elem(1)))
+      |> Enum.product
+    ))
+    |> Enum.sum
+  end
+end