2016 Update

Task/Wireworld/Elixir/wireworld.elixir

@@ -0,0 +1,84 @@
+defmodule Wireworld do
+  @empty      " "
+  @head       "H"
+  @tail       "t"
+  @conductor  "."
+  @neighbours (for x<- -1..1, y <- -1..1, do: {x,y}) -- [{0,0}]
+
+  def set_up(string) do
+    lines = String.split(string, "\n", trim: true)
+    grid = Enum.with_index(lines)
+           |> Enum.flat_map(fn {line,i} ->
+                String.codepoints(line)
+                |> Enum.with_index
+                |> Enum.map(fn {char,j} -> {{i, j}, char} end)
+              end)
+           |> Enum.into(Map.new)
+    width = Enum.map(lines, fn line -> String.length(line) end) |> Enum.max
+    height = length(lines)
+    {grid, width, height}
+  end
+
+  # to string
+  defp to_s(grid, width, height) do
+    Enum.map_join(0..height-1, fn i ->
+      Enum.map_join(0..width-1, fn j -> Map.get(grid, {i,j}, @empty) end) <> "\n"
+    end)
+  end
+
+  # transition all cells simultaneously
+  defp transition(grid) do
+    Enum.into(grid, Map.new, fn {{x, y}, state} ->
+      {{x, y}, transition_cell(grid, state, x, y)}
+    end)
+  end
+
+  # how to transition a single cell
+  defp transition_cell(grid, current, x, y) do
+    case current do
+      @empty -> @empty
+      @head  -> @tail
+      @tail  -> @conductor
+      _      -> if neighbours_with_state(grid, x, y) in 1..2, do: @head, else: @conductor
+    end
+  end
+
+  # given a position in the grid, find the neighbour cells with a particular state
+  def neighbours_with_state(grid, x, y) do
+    Enum.count(@neighbours, fn {dx,dy} -> Map.get(grid, {x+dx, y+dy}) == @head end)
+  end
+
+  # run a simulation up to a limit of transitions, or until a recurring
+  # pattern is found
+  # This will print text to the console
+  def run(string, iterations\\25) do
+    {grid, width, height} = set_up(string)
+    Enum.reduce(0..iterations, {grid, %{}}, fn count,{grd, seen} ->
+      IO.puts "Generation : #{count}"
+      IO.puts to_s(grd, width, height)
+
+      if seen[grd] do
+        IO.puts "I've seen this grid before... after #{count} iterations"
+        exit(:normal)
+      else
+        {transition(grd), Map.put(seen, grd, count)}
+      end
+    end)
+    IO.puts "ran through #{iterations} iterations"
+  end
+end
+
+# this is the "2 Clock generators and an XOR gate" example from the wikipedia page
+text = """
+ ......tH
+.        ......
+ ...Ht...      .
+              ....
+              .  .....
+              ....
+ tH......      .
+.        ......
+ ...Ht...
+"""
+
+Wireworld.run(text)