Functions are the heart of Splus. Nearly everything in Splus is a function. That makes this section rather important.
Functions take zero, one, or more arguments, and return an answer.
Now it's time to explain a bit more about how Splus goes about doing what you type at its prompt. Basically it takes your input line and goes along it, replacing any variables with their value, and working out any functions. Then once it has done all that it usually prints the resulting value. If the line is an assignment, like x , it doesn't print any value. That is actually a function call which has the effect of quitting the system.