Stream: compiler development

Topic: auto inspect on type variables

Brendan Hansknecht (Jan 21 2024 at 18:15):

From #beginners > Type variables implement two abilities?, can we make it so that you never have to specify where a implements Inspect.Inspect.

Make this no longer an error:

» x : a -> Str
… x = \v -> Inspect.toStr v

── TYPE MISMATCH ───────────────────────────────────────────────────────────────

This 1st argument to toStr has an unexpected type:

5│      x = \v -> Inspect.toStr v
                                ^

This v value is a:

    a

But toStr needs its 1st argument to be:

    val where val implements Inspect

All types always implement Inspect, so it should never need to be specified.

Brendan Hansknecht (Jan 21 2024 at 18:16):

I was thinking this probably could be special handling for Inspect.Inspect.

Brendan Hansknecht (Jan 21 2024 at 18:16):

Richard commented that there might be a smarter way to do this:

yeah I think if we expose Inspect.inspect as * -> f where f implements InspectFormatter then Inspect.toStr can be implemented in terms of that and we're good

Brendan Hansknecht (Jan 21 2024 at 18:18):

@Ayaz Hafiz any thoughts on this?

Ayaz Hafiz (Jan 21 2024 at 18:19):

Tbh I wouldn't do this

Ayaz Hafiz (Jan 21 2024 at 18:20):

you could probably special case it but I'm pretty sure it would complicate the implementation

Ayaz Hafiz (Jan 21 2024 at 18:20):

how often is this case going to come up? I think it's likely not that frequent. Adding a suggestion to the error message to add the ability constraint is probably enough.

Ayaz Hafiz (Jan 21 2024 at 18:21):

* -> f where f implements InspectFormatter would not work without punching a hole in the type system

Brendan Hansknecht (Jan 21 2024 at 18:23):

you could probably special case it but I'm pretty sure it would complicate the implementation

Wouldn't be as simple as saying all type variable always implement inspect? Like just appending it to a list?

Ayaz Hafiz (Jan 21 2024 at 19:39):

yes, but that's not a trivial thing. Every type starts off as a variable, so you would have to have the list for every variable.

Brendan Hansknecht (Jan 21 2024 at 20:12):

Make sense. Then nvm.

Brendan Hansknecht (Jan 21 2024 at 20:13):

A nice to have, but definitely not worth any sort of complexity cause it is trivial for an end user to fix and is only hit with type variables

Last updated: Jul 06 2025 at 12:14 UTC