Brendan Hansknecht (Nov 08 2023 at 19:44): Brendan Hansknecht (Nov 08 2023 at 19:44):What would it take to make each of these two types work?
Node : [Branch Str (List Node)]
Node : (Str, List Node)
Fundamentally, I think both of these should be valid. Also, both of them are semi-common issues that users have hit in various cases.
Would these me something that I could just dive into? How complex is the code? Any general thought on path forward/how to implement?
Ayaz Hafiz (Nov 08 2023 at 19:54):Do we know what the specific issue is?
Ayaz Hafiz (Nov 08 2023 at 19:54):I'm actually kind of surprised at least the tag case doesn't work
Brendan Hansknecht (Nov 08 2023 at 19:54):Oh wait.... Is this just never allowed in roc because it would mean that an end user could create a reference cycle which would break roc automatic memory management?
Ayaz Hafiz (Nov 08 2023 at 19:55):How could they create a reference cycle? I think since the language is pure and eager it's impossible to create a cycle
Brendan Hansknecht (Nov 08 2023 at 19:57):Oh yeah, would end up creating a copy in the case I was thinking it would cycle...nvm
Brendan Hansknecht (Nov 08 2023 at 20:00):For Node : (Str, List Node), we say that it needs to be a tag (which in my opinion is wrong, List should count as a break and make that valid)
Brendan Hansknecht (Nov 08 2023 at 20:01):Node : [Branch Str (List Node)] -> Actually, this works. I think I had messed something else up when testing before.
Brendan Hansknecht (Nov 08 2023 at 20:04):Ok. So then I guess the target feature would be allow recursive types if either
Brendan Hansknecht (Nov 08 2023 at 20:04):And 1 already works.
Brendan Hansknecht (Nov 08 2023 at 20:04):I wonder if this is mostly just a case of making the type checker more lax.
Richard Feldman (Nov 08 2023 at 20:05):yeah I also thought this already worked
Richard Feldman (Nov 08 2023 at 20:05):but apparently not!
Ayaz Hafiz (Nov 08 2023 at 21:04):yeah, the fix for the tuple case should be pretty straightforward
Ayaz Hafiz (Nov 08 2023 at 21:05):I guess this probably doesn't work either, right?
W : List W
but that should pass as well (poor man's linked list)
Ayaz Hafiz (Nov 08 2023 at 21:06):(or, poor man's natural number)
Brendan Hansknecht (Nov 08 2023 at 21:41):Cool. I'll look into it. Hopefully it is just a matter of allowing more things in some sort of recursive check or something
Ayaz Hafiz (Nov 08 2023 at 21:45):You'll probably want to look where https://github.com/roc-lang/roc/blob/5fed22405b347707b59fc3ac7608e1e7bb2068e4/crates/compiler/can/src/def.rs#L3282-L3290
is being called in that file, and update the branches that lead to the call site
Ayaz Hafiz (Nov 08 2023 at 21:45):Although, this may end up being trickier than it seems
Ayaz Hafiz (Nov 08 2023 at 21:46):Because changing the restriction is easy, but then the type-checker also needs to be updated to support recursion in a position that's not a recursive tag union
Brendan Hansknecht (Nov 08 2023 at 21:47):Yep
Last updated: Jul 26 2025 at 12:14 UTC