Wrote up a simple test module code (simply called ‘test’), inside which I defined a function mp. It does some loan calculation given a loan amount, interest rate (r) and repayment periods (n).

When I compile the module, I get this error message:

Warning: this expression will fail with a 'badarith' exception

Not really understand what is wrong, I proceed to run the code like so: test:mp(100000, 0.075/12.0, 30*12).

Now I get another error message:

exception error: no function clause matching test:mp(100000, 0.00625, 360)

Turns out the function declaration is mp(B, r, n).

See the problem there? r and n are atoms! I forgot to use uppercase to denote they are actually input variables.