RosettaCodeData/Task/Undefined-values/Sidef/undefined-values.sidef

var x;      # declared, but not defined
x == nil   && say "nil value";
defined(x) || say "undefined";

# Give "x" some value
x = 42;

defined(x) && say "defined";

# Change "x" back to `nil`
x = nil;

defined(x) || say "undefined";