From 3a74f8720abe20f09833da760b334fdc799957ed Mon Sep 17 00:00:00 2001
From: Siraaj Khandkar <siraaj@khandkar.net>
Date: Sat, 21 Jul 2012 03:42:04 -0400
Subject: [PATCH] My first Game of Life!

---
 001/life.erl | 195 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 195 insertions(+)
 create mode 100644 001/life.erl

diff --git a/001/life.erl b/001/life.erl
new file mode 100644
index 0000000..fd3acc9
--- /dev/null
+++ b/001/life.erl
@@ -0,0 +1,195 @@
+-module(life).
+
+-export([main/0
+        ,main/1
+        ]).
+
+
+-define(DIRECTIONS, ['N', 'NE', 'E', 'SE', 'S', 'SW', 'W', 'NW']).
+-define(X, 230).
+-define(Y,  60).
+-define(INTERVAL, 0).  % In milliseconds
+-define(CHAR_DEAD,  <<" ">>).
+-define(CHAR_ALIVE, <<"o">>).
+
+
+main(      ) -> bang(?X, ?Y).
+main([    ]) -> bang(?X, ?Y);
+main([X   ]) -> bang(list_to_integer(X), list_to_integer(X));
+main([X, Y]) -> bang(list_to_integer(X), list_to_integer(Y)).
+
+
+%% ============================================================================
+%% Life processes
+%% ============================================================================
+
+%% ----------------------------------------------------------------------------
+%% Big bang
+%% ----------------------------------------------------------------------------
+
+bang(X, Y) ->
+    N = X * Y,
+    CellIDs = lists:seq(1, N),
+
+    Graph =
+        lists:foldl(
+            fun(ID, Pairs) ->
+                Neighbors = [
+                    integer_to_atom(neighbor_id(D, X, ID))
+                    || D <- ?DIRECTIONS
+                ],
+                [{integer_to_atom(ID), Neighbors} | Pairs]
+            end,
+            [],
+            CellIDs
+        ),
+
+    Parent = self(),
+
+    lists:foreach(
+        fun({ID, Neighbors}) ->
+            register(
+                ID,
+                spawn(fun() -> cell(ID, Parent, Neighbors) end)
+            )
+        end,
+        [{ID, filter_offsides(N, Neighbors)} || {ID, Neighbors} <- Graph]
+    ),
+
+    CellNames = [integer_to_atom(ID) || ID <- CellIDs],
+
+    tick(X, CellNames).
+
+
+%% ----------------------------------------------------------------------------
+%% Tick / tock
+%% ----------------------------------------------------------------------------
+
+tick(X, Cells) ->
+    ok = send_all(Cells, {tick, self()}),
+    All = Cells,
+    Pending = Cells,
+    StatePairs = [],
+    tock(X, All, Pending, StatePairs).
+
+
+tock(X, All, [], StatePairs) ->
+    States =
+        lists:foldl(
+            fun({_ID, State}, States) -> [State | States] end,
+            [],
+            lists:sort(StatePairs)
+        ),
+    ok = do_print_states(X, States),
+    ok = timer:sleep(?INTERVAL),
+    tick(X, All);
+
+tock(X, All, Pending, StatePairs) ->
+    receive
+        {tock, {ID, State}} ->
+            NewPending = lists:delete(ID, Pending),
+            NewStatePairs = [{ID, State} | StatePairs],
+            tock(X, All, NewPending, NewStatePairs)
+    end.
+
+
+%% ----------------------------------------------------------------------------
+%% Cell
+%% ----------------------------------------------------------------------------
+
+% Init
+cell(MyID, MyParent, MyNeighbors) ->
+    MyState = crypto:rand_uniform(0, 2),
+    cell(MyID, MyParent, MyNeighbors, MyState).
+
+
+cell(MyID, MyParent, MyNeighbors, MyState) ->
+    receive
+        {tick, MyParent} ->
+            ok = send_all(MyNeighbors, {request_state, MyID}),
+            cell(MyID, MyParent, MyNeighbors, MyState, {MyNeighbors, []})
+    end.
+
+
+% All neighbors replied
+cell(MyID, MyParent, MyNeighbors, MyState, {[], States}) ->
+    LiveNeighbors = lists:sum(States),
+    MyNewState = new_state(MyState, LiveNeighbors),
+    MyParent ! {tock, {MyID, MyNewState}},
+    cell(MyID, MyParent, MyNeighbors, MyNewState);
+
+% Awaiting requests and replies
+cell(MyID, MyParent, MyNeighbors, MyState, {Pending, States}) ->
+    receive
+        {request_state, ID} ->
+            ID ! {response_state, MyID, MyState},
+            cell(MyID, MyParent, MyNeighbors, MyState, {Pending, States});
+
+        {response_state, ID, State} ->
+            NewPending = lists:delete(ID, Pending),
+            NewStates = [State | States],
+            cell(MyID, MyParent, MyNeighbors, MyState, {NewPending, NewStates})
+    end.
+
+
+%% ============================================================================
+%% Rules
+%% ============================================================================
+
+new_state(1, LiveNeighbors) when LiveNeighbors  <  2 -> 0;
+new_state(1, LiveNeighbors) when LiveNeighbors  <  4 -> 1;
+new_state(1, LiveNeighbors) when LiveNeighbors  >  3 -> 0;
+new_state(0, LiveNeighbors) when LiveNeighbors =:= 3 -> 1;
+new_state(State, _LiveNeighbors) -> State.
+
+
+neighbor_id(Direction, X, I) ->
+    I + offset(Direction, X).
+
+
+offset('N' , X) ->  -X;
+offset('NE', X) -> -(X - 1);
+offset('E' , _) ->       1;
+offset('SE', X) ->   X + 1;
+offset('S' , X) ->   X;
+offset('SW', X) ->   X - 1;
+offset('W' , _) ->      -1;
+offset('NW', X) -> -(X + 1).
+
+
+filter_offsides(N, IDs) ->
+    [ID || ID <- IDs, is_onside(N, atom_to_integer(ID))].
+
+
+is_onside(_, ID) when ID < 1 -> false;
+is_onside(N, ID) when ID > N -> false;
+is_onside(_, _) -> true.
+
+
+%% ============================================================================
+%% Plumbing
+%% ============================================================================
+
+atom_to_integer(Atom) ->
+    list_to_integer(atom_to_list(Atom)).
+
+
+integer_to_atom(Integer) ->
+    list_to_atom(integer_to_list(Integer)).
+
+
+send_all([], _) -> ok;
+send_all([PID | PIDs], Msg) ->
+    PID ! Msg,
+    send_all(PIDs, Msg).
+
+
+do_print_states(_, []) -> ok;
+do_print_states(X, States) ->
+    {XStates, RestStates} = lists:split(X, States),
+    ok = io:format([state_to_char(S) || S <- XStates] ++ "\n"),
+    do_print_states(X, RestStates).
+
+
+state_to_char(0) -> ?CHAR_DEAD;
+state_to_char(1) -> ?CHAR_ALIVE.
-- 
2.20.1