Add Referencing Values In IEx's History as an elixir til

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

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+# 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.