3 ms·

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(...)

• dmitriid 7y ago
  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.
• arthurbrown 7y ago
  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.
• masklinn 7y ago
  > 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 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 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.
  • koolba 7y ago
    I didn’t mean it as a straw man. I’m not familiar with ReasonML at all and meant to illustrate the example.