lec03 generic servers

lectures/03/arithmetic.ex

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+defmodule Arithmetic.Worker do
+    use GenServer
+
+    ### Client API ###
+    def start() do
+        GenServer.start(__MODULE__, nil)
+    end
+
+    def square(pid, x) do
+      GenServer.call(pid, {:square, x})
+    end
+
+    def sqrt(pid, x) do
+      GenServer.call(pid, {:sqrt, x})
+    end
+
+    ### Server Impl ###
+    @impl true
+    def init(_arg) do
+        {:ok, nil}
+    end
+
+    @impl true
+    def handle_call({:square, x}, _from, state) do
+      {:reply, x * x, state}
+    end
+
+    @impl true
+    def handle_call({:sqrt, x}, _from, state) do
+      {:reply, (if x < 0, do: :error, else: :math.sqrt(x)), state}
+    end
+end

lectures/03/counter/.formatter.exs

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+# Used by "mix format"
+[
+  inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
+]

lectures/03/counter/.gitignore

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+# The directory Mix will write compiled artifacts to.
+/_build/
+
+# If you run "mix test --cover", coverage assets end up here.
+/cover/
+
+# The directory Mix downloads your dependencies sources to.
+/deps/
+
+# Where third-party dependencies like ExDoc output generated docs.
+/doc/
+
+# Ignore .fetch files in case you like to edit your project deps locally.
+/.fetch
+
+# If the VM crashes, it generates a dump, let's ignore it too.
+erl_crash.dump
+
+# Also ignore archive artifacts (built via "mix archive.build").
+*.ez
+
+# Ignore package tarball (built via "mix hex.build").
+counter-*.tar
+
+# Temporary files, for example, from tests.
+/tmp/

lectures/03/counter/README.md

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+# Counter
+
+**TODO: Add description**
+
+## Installation
+
+If [available in Hex](https://hex.pm/docs/publish), the package can be installed
+by adding `counter` to your list of dependencies in `mix.exs`:
+
+```elixir
+def deps do
+  [
+    {:counter, "~> 0.1.0"}
+  ]
+end
+```
+
+Documentation can be generated with [ExDoc](https://github.com/elixir-lang/ex_doc)
+and published on [HexDocs](https://hexdocs.pm). Once published, the docs can
+be found at <https://hexdocs.pm/counter>.
+

lectures/03/counter/lib/counter.ex

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+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

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+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

lectures/03/counter/mix.exs

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+defmodule Counter.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :counter,
+      version: "0.1.0",
+      elixir: "~> 1.17",
+      start_permanent: Mix.env() == :prod,
+      deps: deps()
+    ]
+  end
+
+  # Run "mix help compile.app" to learn about applications.
+  def application do
+    [
+      extra_applications: [:logger]
+    ]
+  end
+
+  # Run "mix help deps" to learn about dependencies.
+  defp deps do
+    [
+      # {:dep_from_hexpm, "~> 0.3.0"},
+      # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
+    ]
+  end
+end

lectures/03/counter/test/counter_test.exs

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+defmodule CounterTest do
+  use ExUnit.Case
+  doctest Counter
+
+  test "greets the world" do
+    assert Counter.hello() == :world
+  end
+end

lectures/03/counter/test/test_helper.exs

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+ExUnit.start()

lectures/03/data

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+a12345678 homer simpson comp4958 100 comp4959 49
+a22222222 bart simpson comp2510 99

lectures/03/lec3.ex

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+# how to implement a generic server
+# motivation for GenServer
+defmodule GenericServer do
+  ### Server Implementation ###
+
+  # pass in a module 'm', since module names are just atoms
+  # more generic, take in starting args and pass to modules
+  # init function to do whatever is required beforehand
+  def start(m, arg) do
+    state = m.init(arg)
+    spawn(fn -> loop(m, state) end)
+  end
+
+  defp loop(m, state) do
+    receive do
+      {:call, msg, from} ->
+        {reply, new_state} = m.handle_call(msg, from, state)
+        send(from, {self(), reply})
+        loop(m, new_state)
+
+      {:cast, msg} ->
+        new_state = m.handle_cast(msg, state)
+        loop(m, new_state)
+    end
+  end
+
+  ### Client API ###
+  def call(pid, msg, timeout \\ 5000) do
+    send(pid, {:call, msg, self()})
+
+    receive do
+      # pin operator, reply must have same pid as call argument pid
+      {^pid, x} -> x
+    after
+      timeout ->
+        :timeout
+    end
+  end
+
+  def cast(pid, msg) do
+    send(pid, {:cast, msg})
+  end
+end
+
+defmodule Counter do
+  ### Server Implementation ###
+  def start(file) do
+    GenericServer.start(__MODULE__, file)
+  end
+
+  def init(file) do
+    with {:ok, content} <- File.read(file),
+         {n, _} <- Integer.parse(content) do
+      n
+    end
+    if is_integer(val), do: val, else: 0
+  end
+
+  def handle_call(:value, _from, state) do
+    # -> {reply, new_state} in GenericServer
+    {state, state}
+  end
+
+  def handle_cast({:inc, amt}, state) do
+    state + amt
+  end
+
+  ### Client API ###
+  def value(pid) do
+    GenericServer.call(pid, :value)
+  end
+
+  def inc(pid, amt \\ 1) do
+    GenericServer.cast(pid, {:inc, amt})
+  end
+end

lectures/03/notes.ex

@@ -0,0 +1,25 @@
+### Streams
+
+0..1_000_000 |> Enum.map(& &1 * &1) |> Enum.filter(& rem(&1, 8) == 0) |> Enum.sum
+#                        & &1 * &1 is equivalent to
+#                        fn x -> x * x end
+
+0..1_000_000 |> Steam.map(& &1 * &1) |> Steam.filter(& rem(&1, 8) == 0) |> Enum.sum
+
+fibs = Stream.unfold({0, 1}, fn {a, b} -> {a, {b, a+b}} end)
+fibs |> Enum.take(20);
+
+# fizzbuzz infstream
+nats = Stream.iterate(1, & &1 + 1)
+#      Stream.iterate(1, fn x -> x + 1) is an inf stream because we can take up to n with no limit
+nats |> Enum.take(10)
+
+fizz = Stream.cycle(["", "", "fizz"])
+fizz |> Enum.take(10)
+buzz = Stream.cycle(["", "", "", "", "buzz"])
+buzz |> Enum.take(10)
+
+fizzbuzz = Stream.zip_with([nats, fizz, buzz], fn [n, f, b] ->
+  if f == "" && b == "", do: n,
+  else: f <> b # concat f with b
+end)

lectures/03/rcounter/.formatter.exs

@@ -0,0 +1,4 @@
+# Used by "mix format"
+[
+  inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
+]

lectures/03/rcounter/.gitignore

@@ -0,0 +1,26 @@
+# The directory Mix will write compiled artifacts to.
+/_build/
+
+# If you run "mix test --cover", coverage assets end up here.
+/cover/
+
+# The directory Mix downloads your dependencies sources to.
+/deps/
+
+# Where third-party dependencies like ExDoc output generated docs.
+/doc/
+
+# Ignore .fetch files in case you like to edit your project deps locally.
+/.fetch
+
+# If the VM crashes, it generates a dump, let's ignore it too.
+erl_crash.dump
+
+# Also ignore archive artifacts (built via "mix archive.build").
+*.ez
+
+# Ignore package tarball (built via "mix hex.build").
+rcounter-*.tar
+
+# Temporary files, for example, from tests.
+/tmp/

lectures/03/rcounter/README.md

@@ -0,0 +1,21 @@
+# Rcounter
+
+**TODO: Add description**
+
+## Installation
+
+If [available in Hex](https://hex.pm/docs/publish), the package can be installed
+by adding `rcounter` to your list of dependencies in `mix.exs`:
+
+```elixir
+def deps do
+  [
+    {:rcounter, "~> 0.1.0"}
+  ]
+end
+```
+
+Documentation can be generated with [ExDoc](https://github.com/elixir-lang/ex_doc)
+and published on [HexDocs](https://hexdocs.pm). Once published, the docs can
+be found at <https://hexdocs.pm/rcounter>.
+

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

@@ -0,0 +1,43 @@
+defmodule Counter.Worker do
+    use GenServer # use builtint Elixir Generic Server
+
+    ### Client API ###
+    def inc(amt \\ 1) do
+      GenServer.cast(__MODULE__, {:inc, amt})
+    end
+
+    def dec(amt \\ 1) do
+        GenServer.cast(__MODULE__, {:dec, amt})
+    end
+
+    def value() do
+      GenServer.call(__MODULE__, :value)
+    end
+
+    ### Server Impl ###
+    def start(n \\ 0) do
+        # use module name as name for registered server
+        # now inc, dec, and value dont need pid, and can use __MODULE__
+        GenServer.start(__MODULE__, n, name: __MODULE__)
+    end
+
+    @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

lectures/03/rcounter/mix.exs

@@ -0,0 +1,28 @@
+defmodule Rcounter.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :rcounter,
+      version: "0.1.0",
+      elixir: "~> 1.17",
+      start_permanent: Mix.env() == :prod,
+      deps: deps()
+    ]
+  end
+
+  # Run "mix help compile.app" to learn about applications.
+  def application do
+    [
+      extra_applications: [:logger]
+    ]
+  end
+
+  # Run "mix help deps" to learn about dependencies.
+  defp deps do
+    [
+      # {:dep_from_hexpm, "~> 0.3.0"},
+      # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
+    ]
+  end
+end

lectures/03/rcounter/test/rcounter_test.exs

@@ -0,0 +1,8 @@
+defmodule RcounterTest do
+  use ExUnit.Case
+  doctest Rcounter
+
+  test "greets the world" do
+    assert Rcounter.hello() == :world
+  end
+end

lectures/03/rcounter/test/test_helper.exs

@@ -0,0 +1 @@
+ExUnit.start()

lectures/03/student.ex

@@ -0,0 +1,54 @@
+### Structs
+
+defmodule Name do
+  # defaults to john doe
+  # or without defaults
+  # defstruct [:first, :last]
+  defstruct [first: "john", last: "doe"]
+
+  def new(firstname, lastname) do
+    %Name{first: firstname, last: lastname}
+  end
+end
+
+defmodule Student do
+  # default empty id, default name, default empty score map
+  defstruct [id: "", name: %Name{}, scores: %{}]
+
+  # default scores to empty map
+  def new(id, firstname, lastname, scores \\ %{}) do
+    %Student{id: id, name: Name.new(firstname, lastname), scores: scores}
+  end
+
+  # returns a new map
+  def add_score(%Student{} = s, course, score) do
+    %Student{s | scores: Map.put(s.scores, course, score)}
+  end
+
+  def parse(line) do
+    case String.split(line) do
+      [id, firstname, lastname | rest] ->
+        # chunk_every returns a list of lists
+        scores = for [c, s] <- Enum.chunk_every(rest, 2), into: %{},
+                  do: {c, String.to_integer(s)}
+        Student.new(id, firstname, lastname, scores)
+
+      _ -> :error
+    end
+  end
+
+  def read_data(file) do
+    {:ok, content} = File.read(file)
+    content |> String.split("\n") |> Enum.map(&parse/1) |> Enum.filter(& &1 != :error)
+  end
+end
+
+# s = Student.new("a22222222", "homer", "simpson")
+# # struct pattern matching
+# %Student{id: x} = s
+# x # -> a22222222
+
+# %Student{} = s # doesnt match anything
+#                # but ensures that s is a Student
+
+# Student.add_score(s, "comp4958", 55)