cons, car, and cdr
'(val1 val2 ... valn) - a list of n values.
(list val1 val2 ... valn) - another way that Racket sometimes shows lists.
'null - the empty list.
(cons value lst) - add value to the front of lst.
(cdr lst) - get a list containing all but the first element of lst.
(car lst) - get the first element of lst.
(null? val) - determine if a value is the empty list.
(list? val) - determine if a value is a list.
car and cdr(cadr lst) - get the second element of lst. (Drop one element and then access the first remaining element.)
(cddr lst) - drop the first two elements of lst.
(caddr lst) - get the third element (element 2) of lst.
(caar lst) - get the first element of the first element of lst. Only useful for nested lists.
(list exp1 exp2 ... expn) - create a list by evaluating each of the
expressions and then joining together their values.
(make-list n val) - make a list of n copies of val.
(range n) - create a list of all the natural numbers strictly less
than n (starting with 0).
(range s n) - create a list of all the natural numbers between m
(inclusive) and n (exclusive).
(range s n i) - create a list of all the natural numbers between m
(inclusive) and n (exclusive), incrementing by i each time.
(apply fun lst) - apply the function to all the elements of the
list, en masse.
(filter pred? lst) - Select only the elements of the list for
which the predicate holds.
(map fun lst) - apply the function to each element of the list.
(map fun (list val1 val2 ... valn)) gives you
(list (fun val1) (fun val2) ... (fun valn)).
(map fun lst1 lst2) - create a new list by applying the function to
corresponding pairs of elements from the two lists. You can also use
map with more than two lists.
(reduce binproc lst) - reduce a list to a single value
(sort lst compare?) - sort a list.
(tally predicate? lst) - count how many values meet the predicate.
(length lst) - Determine how many elements are in a list.
(reverse lst) - Create a new list with the elements in the opposite
order.
(append lst1 lst2) - Join two lists together.
(take lst n) - Build a new list consisting of the first n elements
of lst.
(drop lst n) - Build a new list consisting of all but the first n
elements of lst.
(list-ref lst n) - Extract element n of the list. (Remember that
lists start with element 0.)
(index-of val lst) - Determine the position of val in lst. (It
turns out the position is how many values need to be dropped
from lst to reach val.)
(indexes-of lst val) - Find all the indices of the value in the list.
a. If you have not done so already, you may want to open a separate tab or window in your browser for the various readings.
b. Introduce yourself to your partner. Describe your strengths and approaches to work.
c. Update the csc151 library.
d. The person closer to the board is Side A. The other is Side B.
e. Load the lab: list-composition.rkt.
f. Save it as list-composition.rkt.
g. Get started.
As you might guess, one-two-b is the list '(1 2). As you might not have guessed, one-two-a is the value '(1 . 2). That value looks much like a list, but it has a period in the middle. The period is a signal to you that the value is not a list.
Since one-two-a is not a list, it is not possible to reverse it or to append it to another list.
However, like the typical implementation of cons, the typical implementation of append does not confirm that its second parameter is a list. And, like cons, when given a non-list as a second parameter, append returns a non-list. In this case, append returns ‘(0 0 1 . 2). Once again, the period indicates “hey, that’s not a list”.
Why does Scheme permit these non-lists? Because they are a generalization of lists (or at least of the techniques by which we process lists). As we’ll see later in the semester, these non-lists can be quite useful.
Exercises 1–3 from this lab were adapted from a similar lab from Spring 2017.
Exercise 4 was adapated from a similar lab from Spring 2007
Exercises 5–6 were newly written in Spring 2024.
The extra problem was newly written in Spring 2024. However, the sublist problem has appeared throughout the years.