I was watching an elixirconf talk the other day about pipelines and how to handle long pipelines and I learned a really useful coding technique!
\nI typed up this module to demonstrate:
\ndefmodule Brunch do\n def make_bloody_mary(missing_ingredient) do\n IO.inspect(\"Making Brunch:\")\n IO.inspect(\"________\")\n\n with :ok <- add_tomato_juice(missing_ingredient),\n :ok <- add_tobasco_sauce(missing_ingredient),\n :ok <- add_celery_salt(missing_ingredient),\n :ok <- add_horseradish(missing_ingredient),\n :ok <- add_vodka(missing_ingredient) do\n success_step(:ok)\n else\n {:error, :out_of_vodka} -> add_whisky(:ok) |> success_step()\n {:error, message} -> error_step(message)\n _ -> unknown_step()\n end\n end\n\n def add_tomato_juice(_) do\n IO.inspect(\"Adding tomato juice\")\n :ok\n end\n\n def add_tobasco_sauce(_) do\n IO.inspect(\"Adding tobasco sauce\")\n :ok\n end\n\n def add_horseradish(:horseradish) do\n IO.inspect(\"Adding horseradish\")\n {:error, \"You forgot to pick up horseradish!!\"}\n end\n\n def add_horseradish(_) do\n IO.inspect(\"Adding horseradish\")\n :ok\n end\n\n def add_celery_salt(_) do\n IO.inspect(\"Adding celery salt\")\n :ok\n end\n\n def add_vodka(:vodka) do\n IO.inspect(\"Adding vodka.\")\n IO.inspect(\"Oh no! You forgot to pick up vodka!\")\n {:error, :out_of_vodka}\n end\n\n def add_vodka(_) do\n IO.inspect(\"Adding vodka.\")\n :ok\n end\n\n def add_whisky(_) do\n IO.inspect(\"No matter, we can use whisky instead.\")\n :ok\n end\n\n def success_step(_) do\n IO.inspect(\"You did it! Have a great brunch!\")\n IO.inspect(\"\")\n IO.inspect(\"\")\n end\n\n def error_step(message) do\n IO.inspect(\"You have ruined brunch, for reason: \" <> message)\n IO.inspect(\"\")\n IO.inspect(\"\")\n end\n\n def unknown_step() do\n IO.inspect(\"How did this even happen?!?\")\n end\nend\n\nIO.inspect(\n \"When we run this, things did not go as planned. However, we CAN recover from this. So we match on :out_of_vodka in our else block, and add whisky instead.\"\n)\n\nIO.inspect(\"Whisky is better in a bloody mary anyway\")\nBrunch.make_bloody_mary(:vodka)\n\nIO.inspect(\n \"When we run this, we have hit an unrecoverable error, so we handle the error in our else block.\"\n)\n\nBrunch.make_bloody_mary(:horseradish)\n\nIO.inspect(\n \"When we run this, the pipeline goes as expected, and we can enjoy our brunch in peace.\"\n)\n\nBrunch.make_bloody_mary(:all_good)The output looks like this:
\n"When we run this, things did not go as planned. However, we CAN recover from this. So we match on :out_of_vodka in our else block, and add whisky instead."\n"Whisky is better in a bloody mary anyway"\n"Making Brunch:"\n"________"\n"Adding tomato juice"\n"Adding tobasco sauce"\n"Adding celery salt"\n"Adding horseradish"\n"Adding vodka."\n"Oh no! You forgot to pick up vodka!"\n"No matter, we can use whisky instead."\n"You did it! Have a great brunch!"\n""\n""\n"When we run this, we have hit an unrecoverable error, so we handle the error in our else block."\n"Making Brunch:"\n"________"\n"Adding tomato juice"\n"Adding tobasco sauce"\n"Adding celery salt"\n"Adding horseradish"\n"You have ruined brunch, for reason: You forgot to pick up horseradish!!"\n""\n""\n"When we run this, the pipeline goes as expected, and we can enjoy our brunch in peace."\n"Making Brunch:"\n"________"\n"Adding tomato juice"\n"Adding tobasco sauce"\n"Adding celery salt"\n"Adding horseradish"\n"Adding vodka."\n"You did it! Have a great brunch!"\n""\n""