A huge retail store wants a rule engine that qualifies orders’ transactions to discounts based on a set of qualifying rules.And automatically calculates the proper discount based on some calculation rules.

• We can have wrappers of impure functions to interact with the outside world. However, the core logic must be written in a pure functional manner. In the core functional logic:

• Use only vals, no vars allowed.

• No mutable data structures allowed.

• No loops allowed.

• No Null values.

• Make sure all your functions are pure:

o Output depends solely on input.

o Input to the function doesn’t get mutated.

o Has a predictable behavior.