Études for Erlang

Étude 4-3: Non-Tail Recursive Functions

Create a module named powers (no relation to Francis Gary Powers), and write a function named raise/2 which takes parameters X and N and returns the value of X^N.

Here’s the information you need to know to write the function:

• Any number to the power 0 equals 1.
• Any number to the power 1 is that number itself—that stops the recursion.
• When N is positive, XN is equal to X times X(N - 1)— there’s your recursion.
• When N is negative, XN is equal to 1.0 / XN

Note that this function is not tail recursive. Here is some sample output.

1> c(powers).
{ok,powers}
2> powers:raise(5, 1).
5
3> powers:raise(2, 3).
8
4> powers:raise(1.2, 3).
1.728
5> powers:raise(2, 0).
1
6> powers:raise(2, -3).
0.125

See a suggested solution in Appendix A.