A simple language is also a functional language

McKeag, Eves and Rooney’ provide an excellent example of how much can be achieved with a small language. One hopes that their example will inspire more researchers to search for features that can be omitted from a language, instead of features that can be added. By removing unused features from Logo, they have ended by designing a purely functional language, apparently without realizing that this is the case. Many researchers have argued in favour of functional languages, usually for theoretical reasons such as ease of mathematical manipulation (e.g. references 2 and 3). McKeag and company provide a much more practical argument: the assignment statement received little use! Roughly speaking, a functional language is one which prohibits all side effects. Clearly, prohibiting assignment statements matches the functional approach. But, at first sight, the use of commands to move the turtle may seem to violate the functional discipline. How, for instance, can a sequence of commands such as