eval_order.adb

with Ada.Text_IO, Ada.Integer_Text_IO;
use Ada.text_IO;

procedure Eval_Order is
   function Minus(A, B : Integer) return Integer is (A - B);
   
   function Get return Integer is
      R : Integer;
   begin
      Ada.Integer_Text_IO.Get(R);
      return R;
   end;
   
begin
   -- Arguments are evaluated from right to left.
   Put_Line(Integer'Image(Minus(Get, Get)));
end Eval_Order;

$ gnatmake eval_order.adb
gcc -c eval_order.adb
gnatbind -x eval_order.ali
gnatlink eval_order.ali

$ ./eval_order
2 3
 1

ARM 6.4(8/2):

"For the execution of a subprogram call, the name or prefix of the call is evaluated, and each parameter_association is evaluated (see 6.4.1). ... These evaluations are done in an arbitrary order."

(http://www.ada-auth.org/standards/rm12_w_tc1/html/RM-6-4.html)

Your version of GNAT used right-to-left in this case. It might use a different order for a different case. Even if it always uses right-to-left, another compiler, and even another version of GNAT, might use a different order.