Why are patterns in Microsoft.FSharp.Quotations.Patterns double quoted?

Question

The active pattern

Microsoft.FSharp.Quotations.Patterns.``|AddressSet|_|``

has its last element double quoted. Why is it double quoted? What is the use of those quotes?

Answer 1

Typically anything surrounded by double backticks (``...``) is just an identifier that otherwise would not be a valid identifier in the language.

For example, if you want to use a language keyword as a function name (not recommended!) you could escape it in this way. If you didn't use the `` delimiters, this would be a syntax error:

let ``let`` x = printfn "%i" x

``let`` 5
``let`` 8

So in your case, that statement must be appearing in a context where the active pattern syntax is not recognized as being valid. What is the context in which you see it written this way?