> It can be in one of the states > 1. Not Called 2. Calculating the result 3. The result has been calculated. That describes an oracle, not a purely functiona

> It can be in one of the states > 1. Not Called 2. Calculating the result 3. The result has been calculated. That describes an oracle, not a purely functional program. A program describes a process (whether the program is purely functional or totally imperative). The state of the process can be captured in progress because, well, it's a process. There is a series of steps which are applied to produce the calculated result. In purely functional programs, that would be the reduction rules. Each application of a reduction rule produces a new state (in essence the remaining computation to be performed).