When you define a function, you give a list of
parameters that the function takes. These are called the formal
parameters. When you use a function, you give a list of parameters that
the function will use this time. These are called the actual parameters.
The names of the formal parameters and the actual parameters do not need to
match up. You only need to supply the right number of actual parameters in the
right order.
For example, here are two completely equivalent definitions of the function
compound:
compound := (P, R, n) -> P*(1+R)^n;
compound := (Principal, Rate, years) -> Principal * (1 + Rate) ^ years;
Regardless of what symbols are used for the formal parameters, all we need to
know when we use compound is that three actual parameters are
required--the first giving the initial balance, the second giving the interest
rate, and the third giving the number of years.