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

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

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+# 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.