When using with/1 to handle a bunch of matches and things that return {:ok, _} or :error or {:error, _} I often need to differentiate between errors, and I’ll wrap the individual matches in tuples, like this: with( {{:ok, shoes}, _} <- {get_shoes(outfit), :shoes}, {{:ok, shirt}, _} <- {get_sh…

:waving_hand: If you care about specific errors for your conditions, you might be better off with case. case get_shoes(outfit) do {:ok, shoes} -> with {:ok, shirt} <- get_shirt(outfit), true <- shoes_match_shirt?(shoes, shirt) do {:ok, "service allowed"} else …

I think you’re better of returning a more meaningful error from get_shoes/1 Example {:error, {ShoesNotFound, "you forgot your shoes!"}} # or {:error, %ShoesNotFound{message: "you forgot your shoes!"}}

[image] yourpalal: {:ok, _} or :error or {:error, _} The idiom is {:ok, value}, {:error, reason} So the pattern match should focus on the contents of reason. For example: Process.monitor/1 will result in a general message of the format: {:DOWN, ref, :process, object, reason} where reason …

Lots of good ideas from people :slight_smile: I should mention that get_shoes/get_shirt are standins for code from the std. lib, or ecto or plug or whatever. They might be code I own, or maybe not. The idea of improving the error messages is good, and in some cases could be done by changing what fu…

Yes, that’s a good point. One of the things I like about with/1 is that it avoids nesting, but particularly if there are only one or two errors to handle, case could be the way to go (or if!). with also lets me kind of replicate a pattern I like in imperative languages (eg. ruby): shoes = get_shoe…

[image] yourpalal: {{:ok, shoes}, _} <- {get_shoes(outfit), :shoes}, What does the left arrow do there? And where is the documentation for with/1?

with/1 The precedent for the left arrow probably comes from for/1 ; see Pronouncing `<-` - #4 by peerreynders .

Hmmm…I looked in the Kernel docs here: Kernel — Elixir v1.20.2 and there is no with/1. Edit: Ah, I see. It’s listed under Kernel.SpecialForms. And for anyone that cares, the <- operator is discussed on p. 39 of Programming Elixir 1.6 in the section titled “…

with also lets me kind of replicate a pattern I like in imperative languages (eg. ruby): Although not normally used for control flow, you can also throw and raise errors in elixir. shoes = get_shoes() is_nil(shoes) || raise(DressCodeError, "no shoes!") # or shirt = get_shirt() is_nil(shirt) |…

If you ever need more power, you should take a look at GitHub - Nebo15/sage: A dependency-free tool to run distributed transactions in Elixir, inspired by Sagas pattern. · GitHub (Sagas pattern)