A visual demo of Ruby's lazy enumerator
27 comments
·January 8, 2025afraca
drnewman
Laziness is great for collections, and modeling the infinite but as a general model for programming it's a little loopy for my taste too ;-)
whateveracct
That was SPJ being cute more than an actual indictment of Haskell fwiw. That quote gets misused a lot.
Laziness hasn't killed Haskell's usefulness. However, it is something Haskellers take for granted. I can't tell you how many times they "just turn on -XStrict" and are surprised their program gets slower.
adsteel_
Hm, the CSS and JS don't appear to load for me. Not even a <body><html> set of tags in the HTML response.
fredrikholm
Same here, both on computer and mobile. The rest of the website looks fine.
rossta
I have heard a few people mention issues but I haven’t been able to reproduce nor understand the scope of the issue. Any more details you can share? You’re getting HTML but JS or CSS assets aren’t loading, right? What status and headers do you see for static assets?
Syntaf
Really cool visualization and neat to learn about lazy enumeration!
Excuse me while I go back through my code and make sure I’m using lazy enumeration wherever I’m iterating over large collections….
dylan604
This sounds like a similar response I had when learning about stream editors vs text editors. It was one of the killer apps that convinced to become a CLI warrior. Opening up a large text file in Notepad took for ever, but opening the same file in vim was a nothing burger. Then, the same person that showed me that showed me sed/awk/grep, and I was off to the races.
hakunin
Lazy enumeration can also save memory, because you aren’t storing entire collections during intermediate steps, and it works with infinite/unknown size collections. Such as streaming data.
Some examples:
I wrote a utility gem a while ago that lets you lazily intersect, union, etc various potentially infinite streams of data. https://github.com/maxim/enum_utils/
I also used lazy enumeration for traversing the wordmap in my no-RAM static storage gem. https://github.com/maxim/wordmap/
hansvm
In the worst case, that must have intermediate space requirements equal to the entire collections, right?
pyinstallwoes
How is it different than a window, rolling window?
hakunin
It's probably a version of that. But since data is assumed sorted, memory requirements almost never grow beyond one item per stream.
pansa2
So in Ruby, `map` and `select` are eager-by-default, but you can just write `lazy.map().select()` to make the whole chain lazy? That's really nice - much better than Python 2, which was also eager-by-default and you had to change every function call to make it lazy (`map` => `imap`, `filter` => `ifilter`).
Python 3 changed to being lazy-by-default. I assume that improves CPU/memory usage, but in some cases it does have less predictable behaviour. I can see why Ruby, with its goal of "developer happiness", would choose to retain the predictable behaviour of eager-by-default.
saagarjha
Swift does this too, with almost the same syntax. IMO it's the right choice.
thih9
Related discussion from yesterday:
https://news.ycombinator.com/item?id=42652775 (different submitter; 29 points, 3 comments)
endorphine
I was expecting a visual comparison towards the end of the article, where you would be able to click a button and both the eager and lazy versions would start executing simultaneously, one displayed next to the other, and you would clearly see that the lazy one completed earlier. This would make it even more obvious how the lazy one is faster.
Nevertheless, this was great.
rossta
Thanks for the feedback. I was thinking along those lines but settled on a version that let you toggle between the two. I’ll keep this in mind for next time though.
There are probably a lot of fun variations to explore. Since this post seemed to resonate, I may be motivated to try some more experiments.
robocat
I find horizontal/vertical is usually confusing (not to you obviously). Here is an example: https://www.investopedia.com/terms/h/horizontalanalysis.asp Maybe easier to stick with the lazy/eager wording?
rossta
That’s fair. I acknowledge that terms like "horizontal" and "vertical" may be overloaded or even confusing, in this case, if it’s difficult to see the connection with the visuals. This is somewhat part of the risk in trying to explain a concept in a less-than precise way to introduce a new concept.
ryangs
Java Streams and Kotlin Sequences provide similar iterator capabilities. Iterators are great for this lazy performance but can sometimes be difficult to debug. Especially if you are nesting many iterators, then extracting the underlying collection can be complicated. But necessary in many workflows.
lukasb
Apparently Typescript doesn’t have anything built-in like this?
Lio
That's lovely and makes it very obvious what's happening.
When I learned Haskell in college I was blown away by how laziness enables cool things like dealing with infinite lists or more performance even though the UX is exactly the same. (Apparently with Ruby there is the slight hint of adding the lazy method in between)
Later I found out laziness in the whole system by default leads to some difficult issues, which quite a few people seem to agree with. Simon Peyton Jones (Haskell co-creator) apparently has said "The next Haskell will be strict". (https://news.ycombinator.com/item?id=14011943)