The set of result values that the function produces is the range. The function definition expresses how to map each domain value into exactly one range value. Typically, argument values are examined and used without modification. Alternative is Imperative Programming Program creates variables and arrives at an answer through calculations that modify the contents or value of variables through assignment. Most commercially popular languages are imperative.
Programmer has more direct control over the hardware.
Disadvantages Program is no longer a description of how to solve an abstract problem Program is now mixed with statements whose purpose is to obtain the solution in a fast but hardware-specific way. A clever solution for one machine may be worthless on another machine. The empty list null is a special value It is a list, but it is not a pair. Each item in a list is called an element. Each element can be an atom, a structure, or another list.