[HN Gopher] Three Ways to Debug Code in Elixir
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Three Ways to Debug Code in Elixir
Author : clessg
Score : 103 points
Date : 2021-12-04 16:01 UTC (6 hours ago)
(HTM) web link (blog.appsignal.com)
(TXT) w3m dump (blog.appsignal.com)
| marcus_cemes wrote:
| After seeing Elixir pop up so many times on Hacker News these
| last few months, I deicded to give it a go for the Advent of
| Code.
|
| It's been pretty amazing actually, it takes a little getting used
| to, but it really feels like a language that was designed in
| every way possible to be ergonomic and productive. I'm still not
| sure whether it's easier to read purely functional code over a
| few mutable variables and simple loops, especially with a lot of
| filter, reduce, scan, zip, etc.
|
| It's been pretty amazing so far, I haven't gotten further than
| IO.inspect()ing yet. The language server is still leagues even
| behind something like Rust analyzer (even renaming symbols is
| still a work in progress), but it's amazing that such a language
| already has one of the leading web frameworks (Phoenix), and
| despite being very network orientated, it's also excellent at
| solving AoC problems that involve a lot of clever manipulation of
| strings, binary, integers, and the sorts!
| brightball wrote:
| Yea, my experience has been that after getting deep with Elixir
| and understanding how and why it (and the BEAM) works the way
| it does, everything else feels very limiting. Like I know all
| of the problems I'm willingly setting myself up for long term.
| dnautics wrote:
| > It's been pretty amazing so far
|
| Wait till you learn about async tests that are pinned to single
| database checkouts. And -- how async is composable with respect
| to resource pinning. AFAICT no other language does this (not
| even erlang).
| clessg wrote:
| > I deicded to give it a go for the Advent of Code.
|
| That reminds me: in case anyone is curious how that looks in
| practice, it just so happens the creator of Elixir (Jose Valim)
| has been streaming Advent of Code exercises using Elixir (and
| Livebook): https://www.twitch.tv/josevalim
| peoplefromibiza wrote:
| My 2 cents
|
| I've been an Elixir developer for years now, loved it
| immediately and still loving it after all this time.
|
| About refactoring: I've been working as a Java developer for
| the past couple of years and I must admit thaat Intellij does a
| pretty impressive job at helping you refactoring code and their
| code sense is top notch.
|
| But, there's a but.
|
| I've never found myself having to make nuclear refactorings in
| Elixir, not because I don't refactor my code, but because
| modules are self contained and not tied with anything else,
| most of the times it is faster to abstract something over what
| you already have than to refactor all the things.
|
| For example, if you decide that you need a struct instead of
| the old map, you advd a new function that pattern matches on
| the struct and pass it down.
|
| If the struct has a different structure, you process it and
| pass it down.
|
| The "treat data as something that is constantly transformed"
| mentality can take you a long way.
|
| When I can code in java in a way similar to what I do in
| Elixir, things get easier in Java as well.
|
| I miss symbol renaming in Elixir too, but it's never been a big
| stopper in the 6 years I've used it as a primary language.
|
| edit: biggest strength of Elixir is Jose Valim himself. If you
| watch his videos you can see him finding a bug while doing
| something, actually explaining why that's a bug in Elixir (or
| some library) open an issue and ask for PRs
|
| All while showing you complex software patterns that I though I
| could never face before using Elixir.
| marcus_cemes wrote:
| I understand, but a lot of my refactoring is within functions
| to simplify and improve legibility once they work, renaming
| variables with generic names from "result" or "data".
|
| It's a lot faster to do a cheeky F2, knowing that it's not a
| blind find/replace but a static code analysis with the
| ability to understand variable shadowing. Definitely not a
| show stopper though, and it feels more old-school, where
| every letter you type is more meaningful, if that makes
| sense.
|
| And a huge +1 for Jose Valim and the whole community behind
| him!
| michaelterryio wrote:
| Ah, yes, this is how I refactor in Elixir too. I feel icky
| about it from a DRY standpoint but I'm training myself to
| ignore the scolds that held me back from being productive for
| so long.
| ketzo wrote:
| It can't be emphasized enough how good IEx is.
|
| Maybe it's because it is my first experience with a language like
| Elixir, but man, it just feels like I'm _living inside_ the
| program while it's running in a way that an IDE debugger doesn't.
| It's so cool and so powerful.
| marcus_cemes wrote:
| I will never forget the first time I started IEx from within a
| Phoenix project, and found that I had a live shell into the
| running application, while the Phoenix development server was
| running and reachable from the browser, all with hot code
| reloading... No need to create a dummy REST endpoint to try
| running a function.
|
| My mind was blown.
| zorbash wrote:
| Another thing worth trying, is connecting a Livebook instance
| (see: https://livebook.dev/) to a running application. Keep
| in mind Livebook allows for multiple users to work on the
| same notebook at once so this can come handy in pair-
| programming / debugging situations.
| derefr wrote:
| Give a remsh connection to a production cluster, you'll find
| IEx really does mean "living inside" the process--you can reach
| out and add a live trace hook to e.g. a Phoenix Controller
| function, and then immediately see traces from _your live prod
| users_ hitting that trace point. Without recompiling or
| restarting the app--their _existing_ in-memory session state,
| local in-memory caches, etc. are suddenly exposed to you,
| without needing to discard any of it via a redeploy /restart
| and then wait for new user sessions to reproduce the problem.
|
| (You can even redefine the module in-place in memory to see how
| changes affect what you see. Brings a whole new meaning to
| "hotfix": you can do hotfixes that don't even exist on disk!)
| arthurcolle wrote:
| :observer.start is awesome too
| dnautics wrote:
| It's like you are in bash, except you can run real functions,
| and your variables aren't stringly typed.
| dnautics wrote:
| for anyone using Elixir + vscode, this snippet is invaluable:
| { "Inspect": { "prefix": "ins",
| "body": "|> IO.inspect(label: \"$0$TM_LINE_NUMBER\")",
| "description": "Adds a pipeline with a labelled `IO.inspect`",
| } }
|
| when you type ins<tab> it injects a labelled IO.inspect that
| makes it easy to track where the data came from; usually in a
| debugging session the line numbers will be sufficient to track,
| and more importantly, it's almost always easy to ninja out these
| IO.inspects in one shot, because they are almost always the same
| number of characters long (since contiguous line numbers are
| usually in the same decade). Credit goes to one of my former
| junior devs who built this.
|
| video demo: https://www.youtube.com/watch?v=JXQZhyPK3Zw&t=1410s
| (note slickbits doesn't seem to exist anymore)
| mmartinson wrote:
| Recon trace is a worthwhile addition. I've used it for some hairy
| production bugs that don't reproduce locally. Allows you to
| unobtrusively instrument a running system and echo back function
| calls with their params, including process targeting if needed.
|
| There are a number of powerful tools for BEAM runtime tracing. I
| prefer this one because the API is simple enough to commit to
| memory, and it protects against some common foot guns.
|
| https://ferd.github.io/recon/recon_trace.html
| michaelterryio wrote:
| Yep, and here's a nice intro video from this year's ElixirConf:
|
| https://m.youtube.com/watch?v=F7YtYTMud-Y
| jetpackjoe wrote:
| I recently wrote a port of the python IceCream
| project[https://github.com/gruns/icecream].
|
| Feel free to check it out for easier IO.inspect ergonomics:
|
| https://github.com/joseph-lozano/ice_cream
| enraged_camel wrote:
| I don't think I've ever used `IO.puts` for anything. As the
| article notes, `IO.inspect` is far superior.
|
| Also, the Erlang observer is super neat. One really cool thing
| you can do with it is attach it to a _remote_ machine, which
| comes in real handy.
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