Final answer:
The cdr function in Scheme returns the tail of a given non-empty list and does not modify the original list. It's crucial in operating with cons cells and building complex data structures.
Step-by-step explanation:
The cdr function in Scheme does not modify its parameters but instead retrieves a specific part of a given list. Given a non-empty list, cdr returns a list consisting of all but the first element of the original list. In other words, it provides the tail of the list. This function is part of the pair operations in Scheme where lists are constructed using cons cells (a pair of a head and a tail).
For example, if we have a list (1 2 3 4) and we apply the cdr function to it, the result will be (2 3 4). It's important to note that using cdr on an empty list will typically result in an error, and using it on a singleton list (a list with only one element) will give an empty list.