:digraph.add_edge gives unpredictable results when adding an edge, one only knows that the first element in the list will be :"$e" [image] [image] I am trying to create an atomic :digraph.add_vertex+:digraph.add_edge+:dets.insert function. If any clauses in the with statement below fail, I need …

This is a scope problem: rest is not available in the else clauses since it only gets defined when the pattern-matching succeeds. Since you only need it in the insert case, you could pass it in the tuple maybe? {:insert, rest, :dets.insert(...)} Regarding v, it is available in the parent scope, wh…

Elixir works as expected. The bug is in your code. Firstly let’s take a look at the warning. As it says the rest variable is not used inside do … else block. Secondly the value is assigned to variable only on success, so it cannot be used outside of do … else block which contains instructions for su…

yeah I grokked the basics of with statements and liked them so much I wanted to use them extensively. Maybe too extensively! Now I grok them properly. Thank you. Back to good ol’ nested case in this (ahem) case.

[image] sabiwara: PS: Complex else clauses in with can be considered an anti-pattern , maybe this code would actually be clearer with simply nesting case? This way, the necessary variables from intermediate matches would be in scope. Nesting case is also anti-pattern . Since Elixir version 1.12…

[image] Eiji: ~w[a b c]a |> then(fn -> [nil | bc] -> {:ok, {"a is nil", a, bc}} [a | bc] -> {:ok, {"a is not nil", a, bc}} data -> {:error, {"data does not match", data}} end) You might have an arrow too much… it should be fn instead of fn → :slight_smile: Where I could use multiple he…

[image] Eiji: see Kernel.then/2 Did you just tell the guy who wrote it to look it up? :grinning_face_with_smiling_eyes:

[image] kokolegorille: You might have an arrow too much… it should be fn instead of fn → :slight_smile: Thanks, yes I have written it from memory. :sweat_smile: [image] kokolegorille: Where I could use multiple heads anonymous function… I would prefer normal Module function with multiple…

defp atomic_vedge({detspath, graph}, v, parent, meta, ts) do # atomic add of a vertex and its edge to parent and save to dets # if any stage fails preceding successes are rolled back …

[image] vegabook: Looks okay by me the nested case. Thanks for help. Actually I don’t see how this is really an anti-pattern as @Eiji was saying, for modest nesting depths, and Racket people might actually love it :wink: Never heard about “Racket people”. Google also translates racket as same…

I agree that avoiding over-nesting and splitting in small functions is good advice in general. Regarding what the exact maximum nesting level should be, 1 feels quite opinionated. For example, it is quite easy to find examples that are nesting 2 or 3 case expressions within the Elixir codebase. Bu…

For me max indention level should be 4 in most cases, because: I fully agree with credo rule linked above My personal example is pretty simple defmodule Example do # first is obvious for function/macro definition defmacro sample do # similarly this extra indention in macros is obvious …

Pattern matching using [first | rest] in with clause seems to fail?

Questions & Help Questions

adamu December 23, 2023, 8:18am 7

Did you just tell the guy who wrote it to look it up?