title: List basics

We further explore Scheme's list structures. Lists permit us to group data and process those data as a group. We also explore the procedures that we can use with lists, such as range, map, and apply

Useful procedures and notation

Standard list notation

(list v1 v2 ... vk) is a list containing the elements v1, v2, ..., vk.

Creating lists

(list e1 e2 ... ek) returns a list of the elements e1, e2, ..., ek.

(make-list n v) returns a list of n copies of v.

(range n) returns a list of all the natural numbers strictly less than n (starting with 0).

(range s n) returns a list of all the natural numbers between s (inclusive) and n (exclusive).

(range s n i) returns a list of all the natural numbers between s (inclusive) and n (exclusive), incrementing by i each time.

Manipulating lists

(map f l) returns a new list that is the result of applying the function f to each element of the list l. In other words, (map f (list v1 v2 ... vk)) is equivalent to (list (f v1) (f v2) ... (f vk)).

(apply f l) calls variable-argument function f with the elements of l. In other words, (apply f (list v1 v2 ... vk)) is equivalent to (f v1 v2 ... vk).

(map f l1 l2) returns a new list that is the result of applying the binary function f to each of the elements in l1 and l2 element-wise. In other words, (map f (list u1 u2 ... uk) (list v1 v2 ... vk)) is equivalent to (list (f u1 v1) (f u2 v2) ... (f uk vk)).

Other list operations

(length lst) returns the length of list lst.

(reverse lst) returns the list lst but with its elements in reverse order.

(append l1 l2) appends lists l1 and l2 together.

(take lst n) returns a new list consisting of the first n elements of lst.

(drop lst n) returns new list consisting of all but the first n elements of lst.

(list-ref lst n) returns the nth element of list lst, zero index-based.

(index-of val lst) returns the index of the first occurrence of val in list lst.

Preparation

  1. Review the list of procedures above.

  2. If you have not done so already, you may want to open a separate tab or window in your browser for the reading on list basics and the reading on transforming lists.

  3. Load the lab. Remember that the person closer to the board is Side A and the person further fro the board is Side B.

  4. Get started!