Add Match On A Map In A With Construct as an elixir til

README.md

@@ -10,7 +10,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 For a steady stream of TILs from a variety of rocketeers, checkout
 [til.hashrocket.com](https://til.hashrocket.com/).
 
-_776 TILs and counting..._
+_777 TILs and counting..._
 
 ---
 
@@ -142,6 +142,7 @@ _776 TILs and counting..._
 - [Inspecting The Process Message Queue](elixir/inspecting-the-process-message-queue.md)
 - [List Functions For A Module](elixir/list-functions-for-a-module.md)
 - [Listing Files In IEx](elixir/listing-files-in-iex.md)
+- [Match On A Map In A With Construct](elixir/match-on-a-map-in-a-with-construct.md)
 - [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)

elixir/match-on-a-map-in-a-with-construct.md

@@ -0,0 +1,25 @@
+# Match On A Map In A With Construct
+
+Many usage example of the
+[`with`](https://hexdocs.pm/elixir/Kernel.SpecialForms.html#with/1)
+construct show a series of matches on a tuple.
+
+```elixir
+with {:ok, width} <- Map.fetch(opts, :width),
+     {:ok, height} <- Map.fetch(opts, :height) do
+  {:ok, width * height}
+end
+```
+
+You can match on more than just tuples though. Here is how you might match
+on a map.
+
+```elixir
+with %{status_code: 200, body: body} <- HTTPoison.get!(url),
+     {:ok, decoded_body} <- Poison.decode(body) do
+  {:ok, decoded_body}
+end
+```
+
+In fact, you have the full power of Elixir's pattern matching available to
+you in your series of matches for a `with` construct.