CommunityNews

CommunityNews

Tail-call optimization in Elm

What is TCO?

Tail-call optimization (TCO) is a very neat trick that the Elm compiler does to make recursive functions a lot more performant and stackoverflow-proof.

Evan Czaplicki describes it very well in this article and I recommend you go read it. He calls it tail-call elimination but it’s a different name for the same thing.

To summarize Evan’s article, a “tail-call optimized” function is a recursive function that gets compiled to using a loop instead of function calls to itself. Let’s take the following code as an example…

Read in full here:

This thread was posted by one of our members via one of our news source trackers.

Most Liked

OvermindDL1

OvermindDL1

That’s not TCO that Elm does, it’s self-call tail recursive optimization, it only can happen in fully known contexts and is not general enough to be full TCO. Full Tail Call Optimization is where a call is in the tail-most position of a function, that means you can then compile essentially a goto to it (or in the Rust proposal a become for example), this means the call can be dynamically made, can be any amount deep through any amount of function stacks, etc… etc… I really don’t like how the Elm community keeps trying to misrepresent things about the Elm language, it’s an annoying recurring pattern…

In fact, let’s try it, I go to: Try Elm!
And I try running:

import Html exposing (text)

entry f i acc = if i <= 0 then acc else f (i - 1) (acc + i)

dispatch1 i acc = entry dispatch2 i acc

dispatch2 i acc = entry dispatch1 i acc

main =
  let i = dispatch1 10000 0 in
  text (String.fromInt i)

And the result is:

Initialization Error

InternalError: too much recursion

Well, let’s try this in Elixir, a language that DOES support TCO, so the same code ported running through the repl:

❯ iex
Erlang/OTP 24 [RELEASE CANDIDATE 3] [erts-12.0] [source] [64-bit] [smp:16:16] [ds:16:16:10] [async-threads:1] [jit]

Interactive Elixir (1.12.0-rc.1) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> defmodule TestingTCO do
...(1)>   def entry(f, i, acc), do: if(i <= 0, do: acc, else: f.(i-1, acc+i))
...(1)>   
...(1)>   def dispatch1(i, acc), do: entry(&dispatch2/2, i, acc)
...(1)>   
...(1)>   def dispatch2(i, acc), do: entry(&dispatch1/2, i, acc)
...(1)> end
{:module, TestingTCO,
 <<70, 79, 82, 49, 0, 0, 7, 176, 66, 69, 65, 77, 65, 116, 85, 56, 0, 0, 0, 202,
   0, 0, 0, 20, 17, 69, 108, 105, 120, 105, 114, 46, 84, 101, 115, 116, 105,
   110, 103, 84, 67, 79, 8, 95, 95, 105, 110, ...>>, {:dispatch2, 2}}
iex(2)> TestingTCO.dispatch1(10000, 0)
50005000

And since Elixir really does implement TCO and not just a simple recursive loop optimization unlike elm’s communities repeating lies then we can go way way higher!

iex(3)> TestingTCO.dispatch1(1000000, 0)
500000500000

Elm has a lot of issues both as a language and as a community, and passing off a very very common optimization pass performed in almost every language as TCO is just the tip of the iceberg…

AstonJ

AstonJ

Even if it’s not true TCO, performance enhancements are always welcome when it comes to JS land :nerd_face:

rustkas

rustkas

I have already read a lot about the disadvantages of Elm. In your opinion, what is currently better than Elm (in terms of the quality of code generation, what to choose for creating a new application) for the front end part?

Where Next?

Popular Frontend topics Top

First poster: bot
Stock Toolkit: Conclusion :: Brain Dump — Geoff’s Technical Notebook. My toy stock toolkit application is “feature complete” for now. I’...
New
First poster: bot
Vue vs React: Best Choice for Startups. “I just have one question for you: Why Vue? I hope you’re not rolling your eyes thinking - “ah n...
New
First poster: AstonJ
The world of web animations has become a sprawling jungle of tools and technologies. Libraries like GSAP and Framer Motion and React Spri...
New
First poster: bot
Because lighter plugins mean lighter sites. https://vanillalist.top/ This thread was posted by one of our members via one of our news ...
New
First poster: bot
When web accessibility comes to mind most people think of just adding an alt text to an image, but there is much more to it! This article...
New
First poster: bot
Last year I created Pomodone, a small time tracking application based on the Pomodoro technique of working in 25 minute intervals. It’s a...
New
First poster: bot
Add WebAssembly, get performance. Is that how it really works? The incredibly unsatisfying answer is: It depends. It depends on oh-so-ma...
New
First poster: bot
User-preference based media features, container queries, and media queries for new screen types, such as foldable screens, will enable us...
New
First poster: bot
Introduction WebAssembly is a standard of the World Wide Web consortium, which latest official release is WebAssembly Core Specification,...
New
First poster: bot
CSS can be hard to grasp when you’re starting out. It can seem like magic wizardry and you can very easily find yourself playing whack-a-...
New

Other popular topics Top

AstonJ
A thread that every forum needs! Simply post a link to a track on YouTube (or SoundCloud or Vimeo amongst others!) on a separate line an...
New
AstonJ
What chair do you have while working… and why? Is there a ‘best’ type of chair or working position for developers?
New
AstonJ
I ended up cancelling my Moonlander order as I think it’s just going to be a bit too bulky for me. I think the Planck and the Preonic (o...
New
New
Maartz
Hi folks, I don’t know if I saw this here but, here’s a new programming language, called Roc Reminds me a bit of Elm and thus Haskell. ...
New
AstonJ
If you want a quick and easy way to block any website on your Mac using Little Snitch simply… File &gt; New Rule: And select Deny, O...
New
New
New
AstonJ
This is cool! DEEPSEEK-V3 ON M4 MAC: BLAZING FAST INFERENCE ON APPLE SILICON We just witnessed something incredible: the largest open-s...
New
Fl4m3Ph03n1x
Background Lately I am in a quest to find a good quality TTS ai generation tool to run locally in order to create audio for some videos I...
New