[Gretl-devel] default(null) values tests

Dear all, Below there are several additional tests of the default/null values behavior both inside and outside functions. Some results looks strange. 1) With lists (i) in a script nulldata 1 list znull = null isznull = exists(znull) nznull = nelem(znull) print isznull nznull (ii) inside a function function void listtestfun (scalar x, list z[null])   isz = exists(z) nz = nelem(z) print isz nz end function listtestfun(1) We have   isznull =  1.0000000   nznull =  0.0000000 and isz =  1.0000000  nz =  0.0000000 as expected 2) with strings (i) in a script string snull = null issnull = exists(snull) nsnull = strlen(snull) print issnull nsnull The behavior is the same as for lists and is as expected to be Also, emptycheck = snull=="" print emptycheck We see that ' string snull = null' actually creates the "" string (ii) inside a function function void strtestfun (scalar x, string s[null])   iss = exists(s) ns = strlen(s) print iss ns end function strtestfun(1,"oleh") OK! strtestfun(1) we have The symbol 's' is undefined *** error in function strtestfun, line 2 It seems now the problem is not with exists()  but is like this: a function does not defines a string  variable in contrast as it does with default null lists 3) catch string function void testfun3 (scalar x, string s[null])   catch string s err = $error print err  end function  testfun3(1) testfun3(1,"a") Please, explain why we have "0" in the first case and "2" in the second Oleh P.S. I have tried to do something with formatting  but  I have nowhere to check. Please, inform me