Add Compute Intermediate Values In A With Construct as an elixir til

Author: jbranchaud

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/).
 
-_782 TILs and counting..._
+_783 TILs and counting..._
 
 ---
 
@@ -125,6 +125,7 @@ _782 TILs and counting..._
 - [Check For A Substring Match](elixir/check-for-a-substring-match.md)
 - [Check List Membership](elixir/check-list-membership.md)
 - [Comparing DateTime Structs](elixir/comparing-datetime-structs.md)
+- [Compute Intermediate Values In A With Construct](elixir/compute-intermediate-values-in-a-with-construct.md)
 - [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)

elixir/compute-intermediate-values-in-a-with-construct.md

@@ -0,0 +1,23 @@
+# Compute Intermediate Values In A With Construct
+
+The expressions you use in a `with` construct do not have to contain the
+`<-` syntax. You can pattern match and bind values along the way as well.
+
+```elixir
+with %{id: id} <- get_user()
+     url = "/api/#{id}/blogs",
+     %{status_code: 200, body: body} <- HTTPoison.get(url),
+     {:ok, decoded_body} <- Poison.decode(body) do
+  {:ok, decoded_body}
+end
+```
+
+In the above (sorta contrived) example we were able to construct a URL in
+the middle of the series of expressions.
+
+The values we compute inline will be closed into the `with` construct, so
+they won't leak.
+
+See the [`with`
+docs](https://hexdocs.pm/elixir/Kernel.SpecialForms.html#with/1) for more
+details.