lecture 07

.gitignore

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+*.beam

lectures/07/arith.erl

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+-module(arith).
+-export([start/0, square/2, sqrt/2]).
+
+start() ->
+	{ok, _Pid} = spawn(fun loop/0).
+
+square(Pid, N) ->
+	Pid ! {square, self(), N},
+	receive
+		{Pid, Reply} -> Reply
+	end.
+
+sqrt(Pid, N) ->
+	Pid ! {sqrt, self(), N},
+	receive
+		{Pid, Reply} -> Reply
+	end.
+
+loop() ->
+	receive
+		{square, From, N} ->
+			From ! {self(), N * N};
+		{sqrt, From, N} when N < 0 ->
+			From ! {self(), error};
+		{sqrt, From, N} ->
+			From ! {self(), math:sqrt(N)}
+	end,
+	loop().

lectures/07/counter.erl

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+-module(conuter).
+-behaviour(gen_server).
+-export([init/1, handle_cast/2, handle_call/3]).
+-export([start/1, value/1, inc/1, inc/2]).
+
+start(N) ->
+	gen_server.start(?MODULE, N, []).
+
+inc(Pid) -> inc(Pid, 1).
+inc(Pid, Amt) ->
+	gen_server:cast(Pid, {inc, Amt}).
+
+value(Pid) ->
+	gen_server:call(Pid, value).
+
+init(N) ->
+	{ok, N}.
+
+handle_call(value, _From, N) ->
+	{reply, N, N}. % {reply, actual_reply, state}
+
+handle_cast({inc, Amt}, N) ->
+	{noreply, N + Amt}.

lectures/07/counter_supervisor.erl

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+-module(counter_supervisor).
+-behaviour(supervisor).
+-export([start_link/0, init/1]).
+-define(TABLE, counter_table).
+
+start_link() ->
+	ets:new(?TABLE, [named_table, public]),
+	supervisor:start_link({local, ?MODULE}, ?MODULE, []).
+
+init(_) ->
+	Flags = #{strategy => one_for_one},
+	ChildSpecs = [#{id => worker1,
+					staart => {counter_worker, start_link, [0]}}],
+	{ok, {Flags, ChildSpecs}}.

lectures/07/counter_worker.erl

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+-module(counter_worker).
+-behaviour(gen_server).
+-export([init/1, handle_call/3, handle_cast/2]).
+-export([start_link/1, inc/1, value/0]).
+-define(SERVER, ?MODULE).
+-define(TABLE, counter_table).
+
+start_link(N) ->
+	gen_server:start_link({local, ?SERVER}, ?MODULE, N, []).
+
+inc(Amt) ->
+	gen_server:cast(?SERVER, {inc, Amt}).
+
+value() ->
+	gen_server:call(?SERVER, value).
+
+init(N) ->
+	case ets:lookup(?TABLE, value) of
+		[] -> {ok, N};
+		[{_, M} | _] -> {ok, M}
+	end.
+
+handle_call(value, _From, N) ->
+	{reply, N, N}. % {reply, actual_reply, state}
+
+handle_cast({inc, Amt}, N) ->
+	{noreply, N + Amt}.
+
+termintate(_Reason, N) ->
+	ets:insert(?TABLE, {value, N}).

lectures/07/echo.erl

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+-module(echo).
+-export([start/1]).
+
+start(Port) ->
+	Opts = [binary, {active, once}, {packet, line}, {reuseaddr, true}],
+	{ok, Listen} = gen_tcp:listen(Port, Opts),
+	accept(Listen).
+
+accept(Listen) ->
+	{ok, Socket} = gen_tcp:accept(Listen),
+	spawn(fun() -> accept(Listen) end),
+	loop(Socket).
+
+loop(Socket) ->
+	receive
+		{tcp, Socket, Data} ->
+			inet:setopts(Socket, [{active, once}]),
+			gen_tcp:send(Socket, Data),
+			loop(Socket);
+		{tcp_closed, Socket} ->
+			gen_tcp:close(Socket)
+	end.

lectures/07/lec7.erl

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+-module(lec7).
+-export([fact/1, qsort/1, fizzbuzz/1, dedup/1]).
+
+fact(N) when N =< 0 -> 1;
+fact(N) -> N fact(N - 1).
+
+qsort([]) -> [];
+qsort([H | T]) ->
+	qsort([X || X <- T, X =< H]) ++ [H] ++ qsort([X || X <- T, X > H]).
+
+fizzbuzz(N) -> fizzbuzz(1, N);
+fizzbuzz(I, N) when I > N -> ok;
+fizzbuzz(I, N) ->
+	% ~n is newline in erlang, not \n
+	if
+		I rem 15 == 0 -> io.format("fizzbuzz~n");
+		I rem 5 == 0 -> io.format("buzz~n");
+		I rem 3 == 0 -> io.format("fizz~n");
+		true -> io.format("~p~n", [I])
+	end,
+	fizzbuzz(I + 1, N).
+
+dedup([]) -> [];
+dedup([X, X | R]) -> dedup([X|R]);
+dedup([X|R]) -> [X | dedup(R)].
+
+dedup2(L) ->
+	case L of
+		[] -> [];
+		[X, X | R] -> dedup2([X|R]);
+		[X | R] -> [X | dedup2(R)]
+	end.
+
+% compile
+% c(lec7)
+% lec7:fact(100)
+% lec7:qsort([3,2,7,6,8])
+
+F = fun(X) -> X * X end.
+lists:map(F, [1,3,2]).
+lists:map(fun string:length/1, ["hello", "goodbye"]).
+
+% accessing maps
+
+M = #{"bart" => 77, "homer" => 25}.
+#{"homer" := X} = M.
+X.