Question about NOCOPY in function formal parameter

Question

SQL> declare
2 v_1 number(8);
3 procedure p_1(parm_1 in out nocopy number) is
4 begin
5 parm_1 := parm_1 + 50;
6 raise program_error ;
7
8 end;
9 begin
10 v_1 := 100 ;
11 dbms_output.put_line('the value before call is : '|| v_1) ;
12 p_1(v_1) ;
13 dbms_output.put_line('the value after call is : '|| v_1) ;
14 exception
15 when others then
16 dbms_output.put_line('outer exception handle') ;
17 dbms_output.put_line('the value after call is : '|| v_1) ;
18 end;
19 /
the value before call is : 100
outer exception handle
the value after call is : 100
It was said that the keyword NOCOPY made the formal parameter recieve the reference of actual parameter.
my question is : why the value after call is not 150 ?

Answer 1

Thanks ,jeneesh.
I have read the article,but there is a different situation.If there is exception-handling part in the inner block,such as
procedure p_1(parm_1 in out nocopy number) is
begin
parm_1 := parm_1 + 50;
raise program_error ;
exception
when others then
dbms_output.put_line('the value in inter exception is : '|| parm_1) ;
end p_1;
it returns :
the value before call is : 100
the value in inter exception is : 150
the value after call is : 150
So , i put 'raise'
exception
when others then
dbms_output.put_line('the value in inter exception is : '|| parm_1) ;
raise;
end p_1;
it returns
the value before call is : 100
the value in inter exception is : 150
outer exception handle
the value after call is : 100
It conflicts with the formal parameter reference-pass,doesn't it?