jan kili (Jan 02 2022 at 20:49): jan kili (Jan 02 2022 at 20:49):Hey, is it possible to write one function that accepts either a Str or a Num and does different things to them... without requiring tag prefixing?
Brendan Hansknecht (Jan 02 2022 at 20:51):No
Brendan Hansknecht (Jan 02 2022 at 20:51):Would need a tag
jan kili (Jan 02 2022 at 20:51):Hmmm darn
Brendan Hansknecht (Jan 02 2022 at 20:52):At least i can't think of a way.
Brendan Hansknecht (Jan 02 2022 at 20:52):Wouldn't expect a way to exist
Brendan Hansknecht (Jan 02 2022 at 20:52):What are you trying to do?
jan kili (Jan 02 2022 at 20:52):I'm trying to write a pretty printing library that can accept arbitrary data and converts it to a Str, similar to JS's JSON.stringify
jan kili (Jan 02 2022 at 20:53):It works for Str and Num if the user provides a prefix tag to indicate which it is
jan kili (Jan 02 2022 at 20:54):But as soon as you want to stringify a List of strings or numbers... or a Record of anything... The user would have to describe the entire type structure... Which defeats the purpose of a lightweight pretty printer
jan kili (Jan 02 2022 at 20:55):Is a generic Roc pretty printer impossible?
Zeljko Nesic (Jan 02 2022 at 21:57):Yes, trough abilities, aka simplified type classes aka better than interfaces :)
Zeljko Nesic (Jan 02 2022 at 21:57):But they are not implemented yet
jan kili (Jan 02 2022 at 23:48):Could I please see the design doc for abilities? For both library planning and excited curiosity :)
Zeljko Nesic (Jan 03 2022 at 00:02):This was Richard's document, for sure we should organize this knowledge better, but it's still open issue so no sweat.
https://docs.google.com/document/d/1kUh53p1Du3fWP_jZp-sdqwb5C9DuS43YJwXHg1NzETY/edit
Zeljko Nesic (Jan 03 2022 at 00:02):This is conversation thread about them:
https://roc.zulipchat.com/#narrow/stream/304641-ideas/topic/Abilities
Richard Feldman (Jan 03 2022 at 00:34):I want to highlight the last section of that Google doc in particular - my biggest worry about abilities, by far, is that they'll become a source of unnecessary complexity by way of being used for things that had simpler solutions which didn't involve abilities :sweat_smile:
jan kili (Jan 03 2022 at 05:23):Ah, basically OOP leaking in?
jan kili (Jan 03 2022 at 05:24):Great doc, and it sounds like there won't be as strong of a need for a stringify library in the future, thanks to the power of Encode.str!
jan kili (Jan 03 2022 at 05:25):Maybe nonstandard pretty printing will still have its use cases, but I was primarily craving that easy debug logging that JS has, as you mention in the doc
jan kili (Jan 03 2022 at 05:30):Will function definitions be able to use where/has selectors at runtime, similarly to when/is selectors? That might be very helpful.
jan kili (Jan 03 2022 at 05:31):I assume not, since this abilities sounds like a type-level feature and the doc doesn't really reference introspection
Last updated: Jul 26 2025 at 12:14 UTC