TypeScript vs. ReasonML

Re:TypeScript vs. ReasonML by koolba on Wednesday September 04, 2019 @08:56AM (#20876710)

Does ReasonML infer that a type "Product" is the only one in the visible namespace with a "name" property or does it infer at use time that the formatName(...) invocation is valid because the argument has a "name" property?

They're separate concepts. Maybe I want to ensure that I'm receiving a product as it makes no sense to invoke formatName(...) on other things with names like a Cat or Person.

And the generic "thing with a name" one is possible in TypeScript too:

    const formatName = (product: {name: string}) => "Name: " + product.name

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Re:TypeScript vs. ReasonML by masklinn on Wednesday September 04, 2019 @09:28AM (#20876972)

> Does ReasonML infer that a type "Product" is the only one in the visible namespace with a "name" property

Yes.

> does it infer at use time that the formatName(...) invocation is valid because the argument has a "name" property?

No. OCaml does have a structural object system (https://v1.realworldocaml.org/v1/en/html/objects.html) and it is available to reason, but it's syntactically funky (https://reasonml.github.io/docs/en/object) and as far as I can tell TFA does not use it.

> They're separate concepts.

Yes. Which is why OCaml (and thus Reason) separates it[0] from the nominative "structures".

> Maybe I want to ensure that I'm receiving a product as it makes no sense to invoke formatName(...) on other things with names like a Cat or Person.

You're really deep into this strawmanning thing.

[0] pretty completely, you can't use nominative types in a structural context, they are not compatible. In fact structural types are sets of methods, something which doesn't exist on the nominative side.

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Re:TypeScript vs. ReasonML by koolba on Wednesday September 04, 2019 @10:36AM (#20877556)

I didn’t mean it as a straw man. I’m not familiar with ReasonML at all and meant to illustrate the example.

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Re:TypeScript vs. ReasonML by arthurbrown on Wednesday September 04, 2019 @09:22AM (#20876913)

They're different concepts with different ways of being expressed in OCaml.

In this case it truly is a Product and if you want to reuse a field name you'll need to enclose that type in a module.

Row polymorphic -- "thing with a name" -- is possible through the object system which is accessed through a different syntax, and works like go interfaces in practice.

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Re:TypeScript vs. ReasonML by dmitriid on Wednesday September 04, 2019 @09:19AM (#20876901)

IIRC if there are several possible choices, the compiler will complain (with a fairly incomprehensible message), and you will have to explicitly provide the type.

And this happens all the time.

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