Undefined

This value is the result of any operation for which a more sensible result is not available (for example, 1/0 = Undefined). In other words, it is the value of a partial function at points in its domain for which it is not defined.

Variables which are not explicitly initialized, are initialized to Undefined. Hence, it is never an error to assign Undefined to a variable (even though Undefined might not belong to the type of the variable).

Undefined is often used as a substitute for exceptions (which are not supported in Slim). Programs that are still being debugged, can be expected to enter the debugger when an expression results in Undefined.

See also: The ? operator.

Herman Venter
This is Slim documentation as snarfed on 27 May 1999 by dB.