Show how to create a user-defined exception   and   show how to catch an exception raised from several nested calls away.

   Create two user-defined exceptions,   U0   and   U1. 
   Have function   foo   call function   bar   twice.
   Have function   bar   call function   baz. 
   Arrange for function   baz   to raise, or throw exception   U0   on its first call, then exception   U1   on its second.
   Function   foo   should catch only exception   U0,   not   U1.


Show/describe what happens when the program is run.




program ExceptionsInNestedCall;
 
{$APPTYPE CONSOLE}
 
uses SysUtils;
 
type
  U0 = class(Exception)
  end;
  U1 = class(Exception)
  end;
 
procedure Baz(i: Integer);
begin
  if i = 0 then
    raise U0.Create('U0 Error message')
  else
    raise U1.Create('U1 Error message');
end;
 
procedure Bar(i: Integer);
begin
  Baz(i);
end;
 
procedure Foo;
var
  i: Integer;
begin
  for i := 0 to 1 do
  begin
    try
      Bar(i);
    except
      on E: U0 do
        Writeln('Exception ' + E.ClassName + ' caught');
    end;
  end;
end;
 
begin
  Foo;
end.