Visual explanation of why we prepend instead of appending

Anybody wondering why it’s a bad idea to append to lists, when using immutable data? I took a crack at explaining it visually on the Hello World Show Live, recorded at DevConf Poland. Check out that section at and let me know what you think. I’m intending to make it a much better lightning talk I can do at meetups, conferences, etc. (This one was almost totally unrehearsed due to time constraints.)

(Yes it’s static for a while at the start. Hang on. Had a bit of a momentary snag with the slides later in, but got past it. And no, that’s not me in the preview.)


Update: it’s been a while, so I’ve done this talk a few more times (including for an Elixir remote meetup!), so I’ve made a YouTube playlist of the versions of this talk. See Why We Prepend - YouTube for all of them (so far).


This bit made me chuckle Dave … no muss no fuss…

You should definitely consider doing some online courses/vids - I am sure you would make a great teacher :lol:

1 Like

I’ve actually been considering it. Need to get back to someone who asked me if I’d do one on Mutation Testing, and I’m planning a loooong series on making mead! (See Sum of a Batch: ⏯️ Videos for more on that.)