Feature request: PPX support for parametrized types

[benadamstyles]

Would be really helpful if we could do this:

@schema
type thing<'a> = {
  a: 'a,
}

// Would generate:
let thingSchema = aSchema => S.object(s => {
  a: s.field("a", aSchema),
})

and then:

@schema
type parent = {
  property: thing<int>,
}

// Would generate:
let parentSchema = S.object(s => {
  property: s.field("property", thingSchema(S.int),
})

Do you foresee any problems with this idea? Right now I'm just writing this manually each time.

[DZakh]

This sounds like a good idea. I think should be possible to implement

[benadamstyles]

Cool, I might take a shot. Will be complicated by the possibility of multiple type arguments.

[benadamstyles]

Actually I think this will be beyond my capabilities as I imagine it would require tagging types with whether or not they represent parametrized types?

[DZakh]

I think it's not needed. If you find a type declaration with a generic, you turn it into a function with args having the same names as type params. And when you see a type param, you codegen it by the arg name. When a type with generics is used as a field, you turn it into a function call the same as in your example. I don't think there's a need to track anything, just rely on idea that type params are converted to values 'a->a

[benadamstyles]

Ok I think I see, thanks!