Equations are things you can use algebra and calculus on to solve for a particular variable, and obtain a function that tell you the value of that variable based on other values. The vast majority of computer programs do no symbolic manipulation on equations. They calculate, they compare, they store, and they branch. In fact it is a key result of Wolfram's work that once a fairly low level of complexity is reached, a program (in the very very general sense of the word) is hopelessly specialized, and that only very simple combinations of rules result in unexpected and interesting outcomes.