Add Creating A PID as an elixir til

Author: jbranchaud

README.md

@@ -7,7 +7,7 @@ variety of languages and technologies. These are things that don't really
 warrant a full blog post. These are mostly things I learn by pairing with
 smart people at [Hashrocket](http://hashrocket.com/).
 
-_511 TILs and counting..._
+_512 TILs and counting..._
 
 ---
 
@@ -90,6 +90,7 @@ _511 TILs and counting..._
 - [Compute md5 Digest Of A String](elixir/compute-md5-digest-of-a-string.md)
 - [Counting Records With Ecto](elixir/counting-records-with-ecto.md)
 - [Create A Date With The Date Sigil](elixir/create-a-date-with-the-date-sigil.md)
+- [Creating A PID](elixir/creating-a-pid.md)
 - [Creating Indexes With Ecto](elixir/creating-indexes-with-ecto.md)
 - [Determine The Latest Release Of A Hex Package](elixir/determine-the-latest-release-of-a-hex-package.md)
 - [Do You Have The Time?](elixir/do-you-have-the-time.md)

elixir/creating-a-pid.md

@@ -0,0 +1,40 @@
+# Creating A PID
+
+Often times, when invoking a function that spawns a process, the PID of the
+spawned process is returned and we bind to it. That PID is a reference to
+some BEAM process in our system.
+
+We can create our own references using the `pid/3` function.
+
+Let's assume we have the following processes, among others, in our system at
+the moment.
+
+```elixir
+> Process.list |> Enum.reverse |> Enum.take(3)
+[#PID<0.284.0>, #PID<0.283.0>, #PID<0.282.0>]
+```
+
+We can create a reference to any of them using the three number parts that
+they are made up of.
+
+```elixir
+> pid(0, 284, 0)
+#PID<0.284.0>
+```
+
+See, it's alive.
+
+```elixir
+> pid(0, 284, 0) |> Process.alive?
+true
+```
+
+What if we make up a PID that doesn't actually reference any process?
+
+```elixir
+> pid(0, 333, 0) |> Process.alive?
+false
+```
+
+Note: there is also a `pid/1` version of the function. See `h pid` for more
+details.