Lab: Records in Scheme

Summary: We investigate records in Scheme through experiments with a record for chemical compounds.

Contents:

• Exercises
  • Exercise 0: Preparation
  • Exercise 1: Testing Compounds
  • Exercise 2: Selecting Compounds
  • Exercise 3: Falsifying Compounds
  • Exercise 4: A Shirt Record
  • Exercise 5: Searching Shirts
• For Those With Extra Time
  • Extra 1: Sorting Shirts
  • Extra 2: Comparing Records
  • Extra 3: Sorting Shirts, Revisited

Exercises

Exercise 0: Preparation

a. Start DrScheme.

b. Make a copy of compound.scm.

c. Scan through that file to make sure that you understand all the procedures.

Exercise 1: Testing Compounds

a. Try the compoound examples given in the reading on records to see if they behave we I said they would.

b. Try a few of your own variations.

c. Explain why the attempted fake is not listed as a compound. Hint: Think about the order of the let and lambda in compound-type-mark.

Exercise 2: Selecting Compounds

Define a procedure, select-by-color, that takes two arguments -- a list, compounds, of records of type compound and a color symbol -- and returns a list of the names of compounds of that color that are elements of compounds.

Exercise 3: Falsifying Compounds

a. Can you set the melting point of a compound to an illegal temperature? If so, how? If not, why not? (Note that there are other ways to modify compounds than to use the record's provided procedures.)

b. Find a way to make a vector that compound? identifies as a compound. You may not use make-compound or compound-copy to build your new vector. However, you may use either procedure to create a helper compound from which you copy values.

Exercise 4: A Shirt Record

Write a set of definitions for a record type, shirt, to be used in a program that keeps track of the inventory of a clothing store. Provide fields for catalog number, intended gender of wearer, size, color, price, and quantity in stock. Only the last two fields should be mutable.

Exercise 5: Searching Shirts

Adapt the binary search procedure so that it takes two arguments -- a sorted vector, vec, of records of type shirt and a catalog number, catno -- and returns the entire record that contains that catalog number, if there is one in vec, or #f if there is no such record.

For Those With Extra Time

Extra 1: Sorting Shirts

Define a procedure that sorts a vector of records of type shirt into ascending order by catalog number.

Extra 2: Comparing Records

Write an expression that, through an appropriate call to mergesort, sorts a list of shirts by catalog number.

Extra 3: Sorting Shirts, Revisited

Rewrite your answer to the first sorting problem by using your answer to the previous problem.