How to achieve fun[Unevaluated[f][Unevaluated[x], Unevaluated[y]] in a more elegant way?

Question

I have defined a function fun[f_[x_,y_]]. When I call it, I want to wrap everything by Unevaluated:

fun[Unevaluated[f][Unevaluated[x], Unevaluated[y]]

But the above expression looks clumsy, especially if the arguments of fun is more complicated. Is there a more elegant way to do it?

A simple example of the function fun is as follows. The last line is what I expect to get.

fun[f_[x_, y_]] := ToExpression[ToString[f] <> ToString[x] <> ToString[y]]
f = 1; x = 1; y = 1;
fun[f[x, y]]
(* -> 111 *)
fun[Unevaluated[f][Unevaluated[x], Unevaluated[y]]
(* -> fxy *)

I tried several ways by using a single Unevaluated or HoldPattern, and they do not work.

Answer 1

If I understand what you want:

SetAttributes[fun, HoldAll];
fun[expr_] := Identity @@ Identity @@ 
 MapAll[Unevaluated, Hold[expr], Heads -> True]

The two Identity operations fix the fact that MapAll applies Unevaluated to the entire expression as well - MapAll[g, f[x,y]] is g[g[f][g[x],g[y]] when we want g[f][g[x],g[y] - and remove the Hold we artificially put in.