Thanks! For some reason I was looking at an old source file from Cairo.

I don’t really understand the documentation for hash-update! at https://docs.racket-lang.org/reference/hashtables.html?q=string-join#%28def._%28%28lib._racket%2Fprivate%2Fmore-scheme..rkt%29._hash-update%21%29%29 .

Specifically, I wonder if this expression can be simplified by using hash-update!: (hash-set! node-ranks depth (cons node-id (hash-ref node-ranks depth '()))) If not, is there a shorter idiom to achieve what I’m doing here?

@sschwarzer yup, that’s equivalent to (hash-update! node-ranks depth (lambda (ids) (cons node-id ids)) '())

I prefer (hash-update! node-ranks depth (curry cons node-id) '()), but notjack is correct^

if we’re talkin’ lambda sugar: (require fancy-app) (hash-update! node-ranks depth (cons node-id _) '())

FWIW, the update docs do kind of suck—I think they assume you’re familiar with the idea of a hash-update (SML’s maps support something similar), where instead of the new value for a key you give a function that takes in the old value of the key and transforms it. But they don’t actually say that…

Agreed. That explanation could use a rewrite.

I’m gonna update those docs

@ben.knoble https://github.com/racket/racket/pull/3812

That’s already so much better

https://news.ycombinator.com/item?id=26990615

racket in the wild! “A RISC-V core in Racket”