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I think it's best understood if you work backwards from the print calls 1. print is fairly straightforward, prints to stdout what is inputted 2. def area(shape) returns the result of shape call with the two lambda parameters representing the area of a circle as the first parameter, and the second representing the area of a rectangle. 3. def Circle(x,y,r) & def Rectangle(x, y, w, h) are functions which return a lambda that both accepts two parameters, visitCircle and visitRectangle. visitCircle corresponds to the lambda x, y, r : math.pi * r * r in def area(shape). visitRectangle corresponds to the lambda x, y, w, h : w *h in def area(shape). So the def Circle(x, y, r) returns a lambda that takes as input these two formulas, but chooses the formula for calculating a circle's area, whereas def Rectangle(x, y, w, h) takes as input the same two formulas, but chooses the formula for calculating a rectangle's area. |