octavipascual / cis194-introductiontohaskell

🚀Solutions of CIS 194: Introduction to Haskell (Spring 2013) course

CIS 194: Introduction to Haskell (Spring 2013)

In order to learn Haskell I took the CIS 194: Introduction to Haskell (Spring 2013) course.

This repository contains the solutions of each assignment of the course.

Apart from the material of the course, I also checked the following materials:

• Real World Haskell
• Introduction to Functional Programming - TU Delft - edX
• Learn You a Haskell for Great Good!

In addition, since I took the course in an autonomous way, I used some resources to check whether my solutions were correct or not. I always try to solve the problems on my own and I only may take a look if I am really stuck with an exercise. However, when I have already solved the whole assignment, I like to see in detail how others solved it and that makes me learn a lot!

• bschwb cis194-solutions repository
• baugarten CIS-194 repository
• surganov cis914 repository

Finally, I tried to explain how I solved each exercise of the homework to remember how I came to the final solution. Moreover, it may also help the reader to understand the reasoning behind each solution.

Homework 1: Introduction to Haskell

Homework 2: Algebraic Data Types

Homework 3: Recursion patterns, polymorphism, and the Prelude

Homework 4: Higher-order programming and type inference

Homework 5: More polymorphism and type classes

Homework 6: Lazy evaluation

Homework 7: Folds and monoids

Homework 8: IO

Homework 9: Functors

Homework 10: Applicative Functors (part 1)

Homework 11: Applicative Functors (part 2)

Homework 12: Monads

cis194-introductiontohaskell's Issues

A testcase make myFoldl in homework4 fail

Hi,
I find a testcase that make the myFoldl function fail.

(foldr . flip) (++) "A" ["B","C","D"]    -- outputs "ADCB", rather than "ABCD"

What's wrong is after flipping the reduction function, the arguments are swapped, but the order of application is still from right to left.

More explicit,

(foldr . flip) f x0 [x1, x2, x3, x4, x5, ... , xn]
= (f ( ... (f (f x0 xn) xn-1) ... ) x1)

while

foldl f x x0 [x1, x2, x3, x4, x5, ... , xn]
= (f ( ... (f (f x0 x1) x2) ... ) xn)

Incorrect nextLevel function from homework 8

Hi!

Probably I'm a bit late to the Party 😀, but after I've finished the homework, I've decided to take a look at what others have come up with and found your solution. You did a great job with explanations, but the problem is that nextLevel function, even though elegant, doesn't return a correct result.

You version computes the following GuestList if you give it testCompany:

GL [Emp {empName = "Bob", empFun = 2},Emp {empName = "John", empFun = 1},Emp {empName = "Sue", empFun = 5},Emp {empName = "Sarah", empFun = 17}] 25

However, the maximised one is:

GL [Emp {empName = "John", empFun = 1},Emp {empName = "Sue", empFun = 5},Emp {empName = "Fred", empFun = 3},Emp {empName = "Sarah", empFun = 17}] 26

The problem is that you don't check combinations of lists with and without bosses residing in different subtrees, so simply doing mconcat on with and without boss subtrees is not optimal.

I came up with the following solution which gives the right answer:

nextLevel :: Employee -> [(GuestList, GuestList)] -> (GuestList, GuestList)
nextLevel emp xs = (snd best, fst best)
  where best = glCons emp <$> bestSublists
        bestSublists = foldr (\(l, r) (vl, vr) 
                        -> (moreFun (l <> vr) . moreFun (l<>vl) $ r <> vl, r <> vr)) mempty xs

what is the meaning of the exercise 6 of homework 2.

found that your answer is quite excellent but lack the one for exercise 6.

I am confused about the hacker issues.

I am not native English speaker, not sure if it is a joke of the professor or a real question?