Operate

Operate[p, f[x, y, ...]] gives p[f][x, y, ...], applying p to the head of the expression.

Examples

Apply function to head:

Operate[g, f[x, y]]
(* g[f][x, y] *)

Operate[Print, Sin[x]]
(* Print[Sin][x] *)

(* At level 2 *)
Operate[h, f[g[x]], 2]
(* f[h[g]][x] *)

Please visit the official Wolfram Language Reference for more details.