7.2.1 Passing arguments – by position and by keyword

We will consider the previous example again, where the function takes two parameters, namely x1 and x2.

Their names serve to distinguish the two numbers, which in this case cannot be interchanged without altering the result. The first parameter defines the number from which the second parameter is subtracted. When subtract is called, every parameter is replaced by an argument. Only the order of the arguments matters; the arguments can be any object. For instance, we may call the following:

z = 3 
e = subtract(5,z)

Besides this standard way of calling a function, which is bypassing the arguments by position, it might sometimes be convenient to pass arguments using keywords. The names of the parameters are the keywords; consider the following instance:

z = 3 
e = subtract(x2 = z, x1 = 5)

Here, the arguments are assigned to the parameters by name and not by position in the call. Both ways of calling a function can be combined so...