Abstract type support?

[wpcarro]

First of all - thank you for making this and open sourcing it. I'm loving it so far. I'm new to Reason and OCaml so forgive me if the way I phrase this question is vague.

I added a new field to my record that I'm encoding of type StringMap.t(list(string)). When I run milk, I get this error:

Fatal error: exception Failure("Abstract type found, but no 'helpers' module specified for this engine")
Raised at file "stdlib.ml", line 33, characters 17-33
Called from file "src/serde/MakeDeserializer.re", line 131, characters 16-98
Called from file "src/serde/MakeDeserializer.re", line 206, characters 10-20
Called from file "src/serde/MakeDeserializer.re", line 302, characters 16-82
Called from file "belt/belt_List.ml", line 172, characters 29-34
Called from file "src/SerdeFile.re", line 232, characters 12-94
Called from file "src/Milk.re", line 190, characters 12-271
Called from file "src/Milk.re", line 212, characters 4-11
Called from file "src/Milk.re", line 241, characters 10-44
Called from file "bin/Main.re", line 104, characters 4-47

This error goes away when I remove the StringMap.t(..). I'm inferring from the error that the "abstract type" is the StringMap.t and that I need to provide my own serialize and deserialize functions. I think this makes sense. Can you point me to a place in the documentation where I can learn more about doing this? If there isn't any, I'd be happy to write some if you give me a hand.

Thanks!

[wpcarro]

By the way, the StringMap.t was created using what I understand to be OCaml's "module functors":

module StringMap = Map.Make(String);

This is my attempt at getting a general purpose dictionary. I suppose I could also model it as:

type KeywordList('a) = list(("string", 'a))

but I'd rather not since I'll get O(n) performance instead of the log n offered by Map.

[jaredly]

abstract types are definitely supported, but I imagine the error message could be better. Here's an example types.json where "helpers" is provided
https://github.com/jaredly/veoluz/blob/master/types.json#L6
and the TypeHelpers.re that provides serialization and deserialization for the abstract type https://github.com/jaredly/veoluz/blob/master/ui/TypeHelpers.re

[wpcarro]

Thanks for sharing this. So is the advice to add "TypeHelpers" to my types.json file?

[jaredly]

yup! And for the abstract type that you want to support, add manual serialization & deserialization functions. (the example there is for Belt's String Set and String Map)

[wpcarro]

Excellent! Thanks, @jaredly! And thanks for such a great library. As I get more comfortable in this ecosystem, I'd love to contribute.