Question

I’m playing around with quotations and I can’t see an expression pattern for type definitions. Is there really not one, or am I missing something?

<@@ type MyType (name:string) =
    member x.Name = name @@>

Gives “Unexpected keyword ‘type’ in quotation literal.”

Answer 1

You can’t. You can only quote code, that is to say, any valid F# expression. Type definitions are not considered as code, but definitions.

What you might want to do is put ReflectedDefinition attribute on a type members:

type MyType (name : string) =
    [<ReflectedDefinition>] member x.Name = name

If you want to retrieve the AST of members that have ReflectedDefinition you can use Expr.TryGetReflectedDefinition function.

E.g, this sample code prints ASTs of all reflected definition members of MyType:

open Microsoft.FSharp.Quotations
open System.Reflection

type MyType (name : string) =
    [<ReflectedDefinition>] member x.Name = name

let mis = typeof<MyType>.GetMembers()
for mi in mis do
    try
        match Expr.TryGetReflectedDefinition(mi :?> MethodBase) with
        | Some(e) ->  printfn "%A" e
        | None    -> ()
    with _ -> ()
()