More fun with lists

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 val1 val2 ... valn) - a list of n values.

Creating 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.

Manipulating lists

(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 less-than?) - sort a list.

Other list operations

(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.)

Fun higher-order procedures

(lambda (params) body) - a procedure in the standard form. When applied to some values (arguments), substitutes the arguments for the parameters in the body and evaluates the new expression. For example, (lambda (x) (+ x 5)) adds 5 to x.

(o f1 f2 f3 ... fn) - creates a procedure that takes one value and applies fn to that value, then fn-1 to that result, ... then f3to that result, thenf2to that result, and finallyf1to the result, returning the output of f1. For example,(o add1 square)` is a procedure that squares its parameter and then adds 1.

(section expression) - creates a procedure that takes one parameter for each "hole" _. For example, (section (* _ 5)) is a procedure that divides its parameter by 5.

Preparation

  • If you have not done so already, you may want to open a separate tab or window in your browser for the various readings.
  • Introduce yourself to your partner. Describe your strengths and approaches to work.
  • Review the double-dagger problems with your partner.
  • The person closer to the board is Side A. The other is Side B.
  • Load the lab.
  • Get started.