Add elixir genserver example

src/SUMMARY.md

@@ -6,6 +6,8 @@
 
   - [Golang](./dev/golang/main.md)
     - [Testing](./dev/golang/testing.md)
+  - [Elixir](./dev/elixir/main.md)
+    - [GenServer](./dev/elixir/genserver.md)
   - [Rust](./dev/rust/main.md)
     - [serde](./dev/rust/serde.md)
     - [Testing](./dev/rust/testing.md)

src/dev/elixir/genserver.md

@@ -0,0 +1,57 @@
+# GenServer
+
+## How to create a scheduled job (kudos [href](https://github.com/hrefhref))
+
+### Code
+
+```elixir
+defmodule Jobs do
+  # Jobs module is based on GenServer
+  use GenServer
+
+  # Init with `init` as initial value, then continue
+  def init(init) do
+    # call to handle_continue
+    {:ok, init, {:continue, :work}}
+  end
+
+  # Exec the job for the first time, at the end of init
+  def handle_continue(:work, state) do
+    {:noreply, work_then_reschedule(state)}
+  end
+
+  # Exec the job when :work message is received
+  def handle_info(:work, state) do
+    {:noreply, work_then_reschedule(state)}
+  end
+
+  # Get timer from config.exs
+  def get_timer_config() do
+    {:ok, timer} = Application.fetch_env(:app, :timer)
+    timer
+  end
+
+  # Do the important stuff
+  defp work_then_reschedule(state) do
+    # Modify state
+    state = state + 1
+
+    IO.puts(state)
+    IO.puts("Work, then reschedule !")
+
+    # Reschedule, later
+    Process.send_after(self(), :work, get_timer_config() * 1000)
+
+    # Return updated state
+    state
+
+  end
+end
+```
+
+### Usage
+
+```iex
+iex> {:ok, pid} = GenServer.start_link(Jobs, 1)
+{:ok, #PID<0.251.0>}
+```

src/dev/elixir/main.md

@@ -0,0 +1 @@
+# Elixir