PLSQL: For functions like COALESCE(n,m,o,p..) are all n, m, o, p evaluated?

Question

Suppose I only want to pull a number from a sequence if a procedure argument is null:
SELECT COALESCE(in_arg, seq.NEXTVAL) INTO tmp_number FROM dual
Is the nextval always executed, before COALESCE is called?
Same question for logical operators; in oracle do they short circuit?
IF function_one() AND function_two() THEN ...
f1 returns FALSE, does f2 run?

Answer 1

Umm..
With decode its differrent..
SQL> select decode(1,1,1,seq.nextval) from emp;
DECODE(1,1,1,SEQ.NEXTVAL)
                        1
                        1
                        1
                        1
                        1
                        1
                        1
                        1
                        1
                        1
                        1
DECODE(1,1,1,SEQ.NEXTVAL)
                        1
                        1
                        1
                        1
15 rows selected.
SQL> select s.nextval from dual;
   NEXTVAL
         1
SQL> select decode(1,1,1,f2) from dual;
DECODE(1,1,1,F2)
               1