Can I decalre a type of (a -> a)

[Xyncgas]

I tried doing

type Control<`a> = `a -> `a

[jl0pd]

Such kind of questions are better suited for StackOverflow.

Answering question: you can do that, just use quote instead of backtick:

type Control<'a> = 'a -> 'a

Backtick is used when you want to use identifiers with space or other characters, e.g.

let ``weird operator!`` x = x
printfn "%d" (``weird operator!`` 1)

Quote is used when working with generic types https://docs.microsoft.com/en-us/dotnet/fsharp/language-reference/generics/