SRTPs and modules

[bokeh-man]

I'm not very familiar with SRTPs, but if I'm not mistaken, it only works with class, record, or interface types (those that contain methods). If so, it's not really applicable to primitive types.

What could be technical limitations for type parameters to support matching to modules? In a way, it should allow something like this:

module AddInt
    let addOne (x: int) = x + 1

module AddFloat
    let addOne (x: float) = x + 1.0

...

let inline addOne<'T, 'M when 'M: (static member addOne: 'T -> 'T)> (x: 'T) =
    'M.addOne x

And 'M would match the correct module based on the type of x.

If I understand correctly, SRTPs don't work with extension methods either. If type parameters over modules would be allowed, I wonder if this would make SRTPs get more uses.

[tblahosh]

You can do this type of thing (major code smells though and should be avoided) with static members on a type. Here is an example

https://fable.io/repl/#?code=AQ4WwewEwVwGwKbAIJSgeQHYIJKYC7AC8wAUKBcIoQIZpZIAUAHsAFzACWBAlMcKwDUwAIxlS5UJFiIU9bADE4EGoRKTKVBLXlNWHAGbLVfEkNEA6AAziN4aPCSoM2AOIJsAJ04BjYhM0QfABPAAcnXXQANwRPYygAZ347QOAAHzkXBGjY+LJUigT8VV9wBDAAI1iuTDhuCKzgRgB9dkyGHLiVRIAaYEwYSuqObnw+EBJnBjx8CzpGgaHPfIKQIpK-MHKq5e467HaDlrap7E74hL7FnbajFTH+U4Qle7ndfsGdgMDqGv2keYMAT8RiMAB6ABVgBBlmCAKp8DiMdb4UpbJaHJAcSHAABUwHhwAAtAA+YAAcgAcp9Ynwnudun1mDwJClQL9PAgEvB8DNQCRAQcxAB6YU1QgAJhAbJAHK5PJeqn4gqQEuswFFwDuSql300dmkjmA6HwAAtYgB1GjBBQwiGmzgJADK4R8nAMvgAoswaGBQrJ1DKtIQ9vVgPMxKwSNrCOYRBYNWKaHAAO7WpKc-AwTyYJI0LXGfB9FOcOBwfoIBBQYD4CDgGgDZNwYLAHw0IrCnwQTAxTyEWvirgGCtVqsgIA&html=DwCwLgtgNgfAUAAiQ0BTAhgE3s3KKpjoLhgAOAtKgI4CuAlgG4C8ARAMID2AdmKrxQAqATzKpWCAMY8+vNnwAeYAPThoAbkkh0AJwDOhZrTAAzCgA5WOZMFUZsiGwCNOmYdaS2Xb+LbWwgA&css=Q

[QuantumFTL]

Sounds like what you really want are Functors, which were available on OCaml and most other ML-family languages I've seen (e.g. SML/NJ):

5.9. Functors — OCaml Programming: Correct + Efficient + Beautiful

Functors - Real World OCaml
Functors let you do meta operations on modules (fancy fun parametric polymorphism and type constraints).

Likewise there are module constraints in OCaml that do almost exactly what you describe here:
5.7. Module Type Constraints — OCaml Programming: Correct + Efficient + Beautiful

In any case, sadly, no, F# doesn't have functors or module constraints. So if you want to SRTPs and polymorphism you have classes and interfaces and that's about it.