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1 point by Pauan 2376 days ago | link | parent

"Even when I'm programming normally in Arc or JavaScript, I use tables with immutable list keys all the time. It doesn't seem unusual to me."

You silly. Neither JavaScript nor Arc have immutable lists. Well, I guess you could use Object.freeze on an array in JS, but... even if you did that, it would just serialize the array to a string.

3 points by akkartik 2376 days ago | link

Ha, here rocketnia is on my side! I don't need permission from racket or arc or javascript to make a list immutable. I just have to not modify it!


2 points by rocketnia 2376 days ago | link

Lol, yep. The way I "implement" immutable lists in practical programming is by not modifying them. I rationalize that their static type would enforce this if only there were a type system. :-p

More specifically...

In Arc I can't really rely on using lists as keys, since (IIRC) Jarc converts table keys to strings using the same behavior as 'write. However, in practice I have used lists of alphanumeric symbols, since those have a predictable 'write representation on Jarc, a predictable Racket 'equal? behavior on pg-Arc, etc.

Similarly, in JavaScript I tend to use Arrays of strings, storing them as their ECMAScript 5 JSON representation.

  myTable[ JSON.stringify( k ) ] = v;