Add Referencing Values In IEx's History 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/).
 
-_512 TILs and counting..._
+_513 TILs and counting..._
 
 ---
 
@@ -104,6 +104,7 @@ _512 TILs and counting..._
 - [Pattern Matching In Anonymous Functions](elixir/pattern-matching-in-anonymous-functions.md)
 - [Quitting IEx](elixir/quitting-iex.md)
 - [Range Into List Using Comprehensions](elixir/range-into-list-using-comprehensions.md)
+- [Referencing Values In IEx's History](elixir/referencing-values-in-iexs-history.md)
 - [Replace Duplicates In A Keyword List](elixir/replace-duplicates-in-a-keyword-list.md)
 - [Requiring Keys For Structs](elixir/requiring-keys-for-structs.md)
 - [Reversing A List](elixir/reversing-a-list.md)

elixir/referencing-values-in-iexs-history.md

@@ -0,0 +1,44 @@
+# Referencing Values In IEx's History
+
+Each time we execute a statement in an `iex` session, the counter is
+incremented. These numbers are references to the history of the session. We
+can use these references to _refer_ to previously executed values using
+`v/1`. This is particularly handy for multi-line statements or when we
+forget to bind to the result of some function.
+
+Consider the following `iex` session:
+
+```elixir
+iex(1)> :one
+:one
+iex(2)> 1 + 1
+2
+iex(3)> "three" |> String.to_atom()
+:three
+```
+
+If we execute `v()` on its own, it is the same as `v(-1)` in that it will
+give us the latest value in the history.
+
+```elixir
+iex(4)> v()
+:three
+```
+
+Providing any positive number will refer to the references we see next to
+each statement.
+
+```elixir
+iex(5)> v(1)
+:one
+```
+
+Negative numbers, as we saw with `v(-1)`, will count backwards in the
+history from where we are.
+
+```elixir
+iex(6)> v(-4)
+2
+```
+
+See `h v` for more details.