Type control

[salvomic]

hi,
why the IF ELSE control for type control in this program works, but it doesn't works in a non CAS program?

Code:


#cas
multinom(args):=
// multinom(n,{list k_i})
BEGIN
local n, k, argv,argc;
argv:=[args];
argc:=size(argv);
IF argc !=2 THEN
return "Input: integer n, {list k}"; 
ELSE
n:=argv(1);
k:=argv(2);
IF (type(k) != DOM_LIST) THEN return "2nd argument must be a list"; ELSE
 n:= ip(n); k:= ip(k);
 return  n!/∏LIST(k!);
END; // if inner

END; // if out

END;
#end

If I try

Code:


EXPORT Multinomd(n,k,p)
BEGIN
...
IF ((type(k) != DOM_LIST) OR (type(k) != DOM_LIST)) THEN return "2nd and 3rd argument must be a list"; ELSE
...
END;

type(k) control won't be executed, here.
If I use

Code:


EXPORT Multinomd(args)
BEGIN
local argv,argc;
argv:=[args];
argc:=size(argv);
IF argc !=3 THEN
return "Input: integer n, {list k}, {list p}"; 
ELSE
n:=argv(1);
k:=argv(2);
p:=argv(3);
IF ((type(k) != DOM_LIST) OR (type(k) != DOM_LIST)) THEN return "2nd and 3rd argument must be a list"; ELSE
...

END;

the program doesn't work at all, giving "Error: Bad argument value" (I think the logical error is in "argv:= [args]"...: why? this approach works well in the #cas / #end version...

I must control in a 3 arguments if 2nd and 3rd are lists, otherwise return to the user the message that they *must* be lists.

Thank you!