lec03 generic servers

lectures/03/counter/lib/counter.ex

@@ -0,0 +1,18 @@
+defmodule Counter do
+  @moduledoc """
+  Documentation for `Counter`.
+  """
+
+  @doc """
+  Hello world.
+
+  ## Examples
+
+      iex> Counter.hello()
+      :world
+
+  """
+  def hello do
+    :world
+  end
+end

lectures/03/counter/lib/counter/worker.ex

@@ -0,0 +1,41 @@
+defmodule Counter.Worker do
+    use GenServer # use builtint Elixir Generic Server
+
+    ### Client API ###
+    def start(n \\ 0) do
+        GenServer.start(__MODULE__, n)
+    end
+
+    def inc(pid, amt \\ 1) do
+      GenServer.cast(pid, {:inc, amt})
+    end
+
+    def dec(pid, amt \\ 1) do
+        GenServer.cast(pid, {:dec, amt})
+    end
+
+    def value(pid) do
+      GenServer.call(pid, :value)
+    end
+
+    ### Server Impl ###
+    @impl true       # annotation that signature agrees with callback
+    def init(arg) do # arg comes from 2nd arg of GenServer.start
+        {:ok, arg}
+    end
+
+    @impl true
+    def handle_call(:value, _from, state) do
+      {:reply, state, state} # {:reply, actual_reply, new_state}
+    end
+
+    @impl true
+    def handle_cast({:inc, amt}, state) do
+        {:noreply, state + amt} # {:noreply, new_state}
+    end
+
+    @impl true
+    def handle_cast({:dec, amt}, state) do
+        {:noreply, state - amt} # {:noreply, new_state}
+    end
+end