Figure 2: The final function form for areaOfCircle. In this form, there is a line through the middle that separates the form into a top part and a bottom part. The top part defines the representation of all instances of the form and defines the computations for such instances. We interpret the syntactic representation at the top as defining areaOfCircle to be a function of one parameter, identified by the left marker, and returning a single value, identified by the right marker.