Laboratory: Haskell (1)

Summary: We begin our exploration of the Haskell programming language.

Prerequisites: Tate, Sections 8.1 and 8.2.

Contents:

• Preparation
• Exercises
  • Exercise 1: Fibonacci
  • Exercise 2: Reversing Lists
  • Exercise 3: List Utilities
  • Exercise 4: Fibonacci, Revisited
  • Exercise 5: Polyexpressionism
  • Exercise 6: Reversing Lists
  • Exercise 7: Pairing Colors
• For Those with Extra Time

Preparation

a. Create a directory for the lab.

b. Open a browser window on Tate's examples, in case you want to try any of them.

Exercises

Exercise 1: Fibonacci

Explore each of Tate's Fibonacci examples and verify that they work the way you expect.

Exercise 2: Reversing Lists

This exercise is taken from Tate.

Write a function that computes the reverse of a list.

Exercise 3: List Utilities

a. Write mytake n lst, which extracts the first n elements of a list.

b. Write mydrop n lst, which drops the first n elements of a list.

c. Write mynth n lst, which computes the nth element of a list.

Exercise 4: Fibonacci, Revisited

At some point, you may have noted that it's a bit strange that fib is defined as a function, given that we normally talk about the Fibonacci sequence. Write a recursive definition of the sequence.

In Lazy Scheme, we might write this as

(define fib
  (cons 1 (cons 1 (map + fib (cdr fb)))))

You may find the following definition helpful.

module Main where
  map2 f [] [] = []
  map2 f (x:xs) (y:ys) = (f x y):(map2 f xs ys)

Exercise 5: Polyexpressionism

This exercise is taken from Tate.

Write allEven in as many ways as you can.

Exercise 6: Reversing Lists

This exercise is taken from Tate.

Write a list comprehension to build a childhood multiplication table. The table would be a list of three-tuples where the first two are integers from 1-12 and the third is the product of the first two.

Exercise 7: Pairing Colors

This exercise is taken from Tate.

Write a function that builds two-tuples with all possible combinations of two of the colors black, white, blue, yellow, and red. Note that you should only include one of (black, blue) and (blue, black).

For Those with Extra Time

If you find yourself with extra time, begin reading the next section of Tate.