Haskell Fall 2023

Haskell course homework

How to pass the course

• homework
  • after each lecture | 10 points max
  • deadline: Thursday 23:59 | 0 points per task after the deadline
  • 1 week to fix my comments | all comments fixed -> full grade.
  • write tests | no tests -> your grade goes down
  • project can be built and tests work | build/tests fail to my review -> -2 points
    • write me before opening PR if you can't solve the problem
  • use hlint and -Wall | not explained compiler warnings and hlint recommendations -> -1 point
  • do not pass solutions to each other | explicit reuse -> 0 points per task
    • write me before opening PR if you struggle with the task and want to get a hint
  • Once a semester, you may pass homework after the deadline (no more than 1 week later) and get a full grade
• exam
  • theory + practice
• [grade for the course] = [average homework grade] * 0.5 + [exam] * 0.5

How to pass your homework

1. Fork this repo -- each branch contains the homework for the corresponding lecture
2. Create a branch hw<x> and your project directory hw<x>, where x `elem` [1..12]
3. As you complete the assignment
   • check you have no compiler warnings and all tests pass: cabal clean && cabal test
   • all hlint hints are fixed: hlint .
   • open the PR in this repo
   • the PR should be named: <HW###>, <LastName_FirstName>
4. I review your PR and leave my comments: accepted or requires fixes

---

Program

1 lecture

Introduction

• Motivation for learning Haskell
• FP core concepts
  • immutability
  • recursion
  • high-order functions
  • pattern matching
  • currying
• Haskell core concepts
  • Functional
  • Statically typed
  • Pure
  • Type inference
  • Concurrent
  • Lazy
  • Packages
• Comparison with other languages
• Motivation to use Haskell
  • Memory safety
  • High performance
  • Bugs are caught early & Explicit data model
  • Correct software
  • Ease of refactoring & Composability
  • Well-developed ecosystem
• What to read about Haskell
• History

Basics I

• Terms & their properties
  • associativity
  • binding order is unimportant
  • immutability
  • lazy by default
• Binding
  • global & local
  • let, where
• Functions (+ lambdas)
• Pattern-matching (+ case of)
• Branching
  • if-then-else
  • guards
• Operators
• Currying
• Recursion & Tail recursion
• Types
  • Base types (Bool, Char, Int, Integer, Float, Double, T1 -> T2, (T1, T2, ..., Tn), (), [T])
  • Type constraints
  • Custom types
  • Standard module types (Maybe, Either, list, tuple)

2 lecture

Environment and project

• GHC & GHCi
• Packages и Hackage
• Build Tools (stack & cabal)
• Project creation and its structure
• Haskell Language Server (HLS)
• GHCup

Code

• HLint
• Haskell API search engine hoogle
• Standard module Prelude
• HSpec
• Pragmas
  • TupleSections
  • LambdaCase

Basics II

• list comprehension
• foldr / foldl / foldl1

---

3 lecture

Type Classes

• Type class
• Polymoprhism
  • Parametric
  • Ad-hoc
• Class instance instance
• Standard type classes (Eq, Ord, Num, Show, Read)
• deriving
• Type classes for high order types
• Type classes are syntax sugar

Data Types

• ADT
• Records
• Pragmas
  • RecordWildCards
• data vs newtype vs type

Point-free style

• Operators
  • function application $
  • reversed function application &
  • function composition .

---

4 lecture

List-like data structures

• What the lists are in reality
• Other types
  • Text
  • String
  • Vector
  • Set
  • Map
• foldl / foldr for other types

Haskell in BIOCAD

---

5 lecture

Monoid and friends

• Magma
• Semigroup
• Monoid

Foldable

Functor

---

6 lecture

Functors

• Functor
• Applicative
• The meaning of f <$> x <*> y <*> z

Applicative parsers I

• Parser definition

  newtype Parser tok a 
      = Parser { runParser :: [tok] -> Maybe (a, [tok])}

• Functor for Parser
• Applicative for Parser
• Examples of simple parsers

---

7 lecture

Applicative parsers II

• Alternative for Parser
• Parser for CSV

Monads I

• Random generation in Haskell
• Monad
• Evaluation context
  • Maybe, [], Either, Reader, `Writer``
  • Kleisli arrow

---

8 lecture

Monads II

• Генератор псевдослучайных чисел
• Traversable
• Identity monad
• do-notation
• MonadFail
• Maybe, []
• Writer, Reader

---

9 lecture

Monads III

• About Maybe, Either, []
• Writer, Reader
• State

---

10 lecture

Monads IV

• State
• IO

---

11 lecture

Laziness and eager Haskell [source]

• Evaluation strategies: call-by-need vs call-by-value
• NF vs WHNF
• thunks
• BangPatterns extension
• UNPACK and unboxed types
• $! and seq

---

12 lecture

Monad Transformers

• MaybeT
• Type class MonadTrans
• Own monad transformer
• ExceptT, ReaderT, WriterT, StateT
• packages transformer vs mtl

---

13 lecture (extra)

• homework legacy
  • buildHeap
  • laziness and exceptions
  • questions
• Comondas
• ML in Haskell
• GHC