KamilLelonek · May 17, 2020 10:56 · May 17, 2020
diff --git a/download.ex b/download.ex
@@ -0,0 +1,20 @@
+defmodule Download do
+  use Pipe
+
+  def start(api_key) do
+    api_key
+    ~> download()
+    ~> parse()
+  end
+
+  defp download(123), do: {:ok, "valid result"}
+  defp download(_), do: {:error, "invalid API key"}
+
+  defp parse({:ok, message}), do: %{message: message, downloaded_at: Time.utc_now()}
+end
+
+Download.start(123)
+#=> %{downloaded_at: ~T[10:53:31.643047], message: "valid result"}
+
+Download.start("invalid") |> IO.inspect()
+#=> {:error, "invalid API key"}
diff --git a/pipe.ex b/pipe.ex
@@ -0,0 +1,21 @@
+defmodule Pipe do
+  defmacro __using__(_) do
+    quote do
+      require unquote(__MODULE__)
+
+      import unquote(__MODULE__)
+    end
+  end
+
+  defmacro left ~> right do
+    quote do
+      case unquote(left) do
+        {:error, error} ->
+          {:error, error}
+
+        result ->
+          result |> unquote(right)
+      end
+    end
+  end
+end
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