Help with stringify and result mapping · beginners

Hi, I'm trying to convert some example code that munges on a data model with optionals and errors. I may have skimmed over it in the tutorial, and maybe it relates to encoders, but how do I just write structured data to stdout in an easy fashion? Example of what I'd like to do here:

https://github.com/contextfreecode/rocdemo/blob/0e7ee7c346d220c7ac29bb2c90353b85521d9ada/main.roc#L55

Also, I made some Result mapping helpers at the bottom of this file. Is anything built-in that I've missed? Using when for everything is bulky. And I see some related looking things on cli Task (like map and mapErr), but I haven't simulated using Task for my simulated network reading, and I'm not sure if that would be the right things anyway.

Thanks!

Tom (Nov 18 2023 at 22:22):

Also, since I'm modeling data with optionals, I couldn't use optional record fields. So I used Err {} for none. I tried saying null = Err {}, but it seemed to fail at row polymorphism. Any way to define a row polymorphic constant like this?

Brendan Hansknecht (Nov 18 2023 at 22:35):

but how do I just write structured data to stdout in an easy fashion?

We have a partially implemented but not complete inspect ability that plans to be autoderived that would enable this. Until then, manually writing a function or using a encoder is the best option.

Is anything built-in that I've missed?

Result as map, mapErr, try, and onErr. With backpassing, that tends to avoid both deep nesting and lots of when .. is expressions. https://www.roc-lang.org/builtins/Result

Any way to define a row polymorphic constant like this?

I am pretty the answer is that there is no way to do that. It would have to be a function that returns the value to get the results you expect.

Tom (Nov 18 2023 at 22:39):

Wow, I managed to overlook the Result section there. Thanks for that and the other info!

Luke Boswell (Nov 18 2023 at 22:48):

I thought Inspect works ok, is there anything still outstanding with that? Here is the example https://github.com/roc-lang/roc/blob/main/examples/inspect-logging.roc

Luke Boswell (Nov 18 2023 at 22:48):

$ roc run examples/inspect-logging.roc
{people: [{firstName: "John", lastName: "Smith", age: 27, hasBeard: true, favoriteColor: Blue}, {firstName: "Debby", lastName: "Johnson", age: 47, hasBeard: false, favoriteColor: Green}, {firstName: "Jane", lastName: "Doe", age: 33, hasBeard: false, favoriteColor: (RGB (255, 255, 0))}], friends: [{2}, {2}, {0, 1}]}