CS 330: Lecture 29 – Haskell IO
Dear students, Up till this point we haven’t written any standalone programs—none that get input from the user, none that generate output. We have looked at the purely functional side of Haskell, where time does not exist. Functions always produce the same value given the same inputs. No matter how many times you call it. […]
CS 330: Lecture 28 – Filter, Map, and Fold
Dear students: Last time we talked about lambdas and higher-order functions. We wrote this count method: count :: (a -> Bool) -> [a] -> Int count _ [] = 0 count predicate (first : rest) | predicate first = 1 + count predicate rest | otherwise = count predicate rest Let’s start with a Program […]
CS 318: Lab 20 – Animations
Dear students, Today we explore transitions to add a little life to our webpages using CSS transitions. As an example, we’ll create a list whose items pop out when hovered. We start with a list: <ul> <li>one</li> <li>two</li> <li>three</li> <li>four</li> </ul> Let’s add some background color to each item: li { background-color: blue; color: white; […]
CS 330: Lecture 27 – Lambdas and Higher-Order Functions
Dear students: Let’s start with a Program This: Using composition and point-free style, write a function that yields the square of the elements’ sum. Using sum and ^. It might help to start without composition and point-free style. Here’s my solution. squaredSum :: Num a => [a] -> a squaredSum list = sum list ^ […]
Multiple Assignment in Twoville
As I dream up animations in Twoville, I find myself generating a lot of shapes that share properties with other shapes. For instance, these two circles have the same radius and color: a = circle() b = circle() a.radius = 10 b.radius = 10 a.rgb = [1, 1, 0] b.rgb = [1, 1, 0] I […]
CS 330: Lecture 26 – Ways of Making Functions: Composition and Lambdas
Dear students: There are at least four ways of defining functions in Haskell: by defining a named abstraction of some algorithm by partially applying parameters to an existing function to get a new function expecting only the remaining parameters by composing a gauntlet of functions together by defining unnamed lambdas We’ve seen the first two. […]
CS 318: Lab 19 – Forms
Dear students, Thus far we have focused on one half of the communication process: the “speaking” of our ideas to our sites’ visitors. Generally this is not enough. We would like to hear back from our visitors. We want them to join a mailing list, make an order, contribute an idea, vote, and who knows […]
CS 330: Lecture 25 – Ways of Making Functions: Composition
Dear students: Let’s warm back up to Haskell by writing some functions to review the ideas we’ve seen in Haskell so far. Here’s our first: Given three points in 2D space, find a fourth which forms a parallelogram. There are many possible answers to this. The trick is to find the vector between two of […]
CS 318: Lab 18 – Tabbed Viewing
Dear students, Last time we started implementing dropdown menus. We decided to continue that effort today, though I do want to add one extra and related exercised: a tabbed viewer. Here’s your TODO list: Breathe easy! See you next time! Sincerely, Lab First, we finish up our lab 17 exercise on switching between small and […]
With Blocks in Twoville
In my software engineering class in college, Dr. Drake dropped on us a half-written piece of software that managed a database of movies. Our challenge was to improve it. It was the first and only time I’ve touched Visual Basic, and I remember only one thing about the project and the language: with-statements. Suppose you’re […]