OCaml at Bloomberg

Re:OCaml at Bloomberg by gopiandcode on Monday August 23, 2021 @07:38PM (#28283435)

It feels somewhat disingenuous to include a turing-complete meta-programming language (i.e macros) in your definition of the C++ type system.

Because vanilla OCaml doesn't have any mechanism for expressing compile-time computations, the same level of transformations aren't possible, but I wouldn't call this a limitation of the type-system, rather the meta-programming capabilities.

Although, you can somewhat approximate it with modules and functors:

     module type M = sig type t val t: t end

     let my_type (type a) (v: a) : (module M) =
       let module M = struct
         type t = a
         let t = v
       end in
       (module M : M)

     module T1 = (val my_type 123)
     type t1 = T1.t
     let val1 : t1 = T1.t
     module T2 = (val my_type val1)
     type t2 = T2.t

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Re:OCaml at Bloomberg by jcelerier on Tuesday August 24, 2021 @12:54AM (#28285225)

> It feels somewhat disingenuous to include a turing-complete meta-programming language (i.e macros) in your definition of the C++ type system.

But this is literally what a type system is about ? TS definitions don't care about compile-time and run-time ; what you call "macros" are type-level functions which are a byproduct of the expressivity of C++'s TS.

Remember that expressivity of a type system is just the cardinality of the type set you can express with it.

Type systems where you can parametrize on nothing are less expressive than type systems that can parametrize on types, which are less expressive than TS which can parametrize on meta-types, which are less expressive than TS which can parametrize on meta-types and integers (C++98, Haskell afaik), which are less expressive than TS which can parametrize on meta-types and arbitrary compile-time values (C++20, soon Rust I believe ?), which I'd guess are less expressive than full-blown dependent types but I'd need to check the exact definition

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Re:OCaml at Bloomberg by pjmlp on Tuesday August 24, 2021 @01:19AM (#28285360)

Actually you can extend OCaml with similar mechanisms via ppx, apparently op isn't aware of it.

https://ocamlverse.github.io/content/metaprogramming.html

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Re:OCaml at Bloomberg by jcelerier on Tuesday August 24, 2021 @01:42AM (#28285484)

TIL about it, last time I wrote some OCaml camlp4 was still all the rage

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Re:OCaml at Bloomberg by pjmlp on Tuesday August 24, 2021 @02:42AM (#28285793)

Yeah, it was decided to merge efforts and integrate into the compiler around the time the Real World OCaml book came out.

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Re:OCaml at Bloomberg by bradrn on Tuesday August 24, 2021 @11:26AM (#28290101)

> TS which can parametrize on meta-types and integers (C++98, Haskell afaik)

Haskell also supports type-level strings and type errors, as well as arbitrary ADTs if defined with the -XDataKinds extension enabled. Not sure what you mean by ‘parametrizing on meta-types’ though.

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Re:OCaml at Bloomberg by carnitine on Tuesday August 24, 2021 @03:43AM (#28286051)

Where does that definition of expressivity come from? As far as I can tell the cardinality of the ‘type set’ is omega_0 in both C++ and OCaml.

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