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Having fun with Haskell
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haskell.md

Tiny Haskell Essay

created: 01.FEB.2024

I love to learn new programing languages, it help to open the mind to new possibilities and compare different approaches. For instance, I learned Ruby and Scala in 2010, Clojure and Haskell in 2011, Go in 2015, Kotlin 2016, Rust in 2018 and Idris, TypeScript in 2019, 2020 Pandemic strike did a bunch of pocs but not with new langs(crazy year), Zig in 2021, 2022(coding in lots of langs but nothing new) - in 2023 I'm learning Nim and V. Learn at least one lang per year. This post is not complain, it's just to share some toughts, notes and impressions.

Why Haskell

  • Created in 1990 (30+ years)
  • Designed by many people
  • PURELY Functional Programing
  • Statically Typed
  • Compiled
  • Fun after some digestion time
  • Concise
  • Much more with less
  • REPL (ghci) like all good FP langs
  • Solid but yeat not everywhere - very niche
  • Lots of libs with package management (cabal)
  • Scala and F# was heavily inspired by Haskell
  • There are some use cases on Facebook, Github, Target and other companies but mostley academia.
  • List of some companies That Use Haskell in Production https://serokell.io/blog/top-software-written-in-haskell
  • Nothing weired around strings like in rust and zig.
  • There is not loop in haskell you need to use functions and function composition with map, filter, foldl.
  • Syntax is terse, meaning spaces are separators between function parameters
  • Types Philosophy: Don't think about types belonging to a big hierarchy of types. Instead, we think about what the types can act like and then connect them with the appropriate typeclasses

My Feelings (01.FEV.2024 )

  • First time I saw haskell was in 2006 and I was not impressed neither scared.
  • Them because Scala in 2010, I went to haskell again, that time was a bit scarry
  • Over the year I revised haskell time to time, now collecting my last review in 2024
  • No fear, no issues jun fun :-)
  • Haskell is not weidely adopted in the industry besides some big companies using it
  • People complain in too much academia thing
  • But haskell diserves respect is a base for so many modern langs
  • Syntax and ideas are amazing.
  • But Diego - I dont get Functors, Applicatives, Monoids and Monads - Read this https://www.adit.io/posts/2013-04-17-functors,_applicatives,_and_monads_in_pictures.html functor-applicatives-monodas

Show me the code

My POCs with Haskell: https://github.com/diegopacheco/haskell-playground
Try haskell: https://tryhaskell.org/

1 - Here is a simple function

factorial 0 = 1
factorial n = n * factorial (n - 1)

2 - IFs can be returned or assined to variables

To assign anything to variable use let or just return in the function boddy if you want

doubleSmallNumber x = if x > 100
                        then x
                        else x*2

3 - Easy to work with collections

let lostNumbers = [4,8,15,16,23,42]     -- creates a List
let result = [1,2,3,4] ++ [9,10,11,12]  -- concat 2 lists 
let out = "Steve Buscemi" !! 6          -- gets element out by index
let rev = reverse [5,4,3,2,1]           -- reverse the list
let thr = take 3 [5,4,3,2,1]            -- take 3 elements from the list
let h   = head [5,4,3,2,1]              -- get the first element
let l   = last [5,4,3,2,1]              -- get the last element
let gotit = 4 `elem` [3,4,5,6]          -- is 4 in the list? yes

plenty of useful functions like: product, minimum, sum, drop, etc...

4 - Ranges

This are utilities that make working with lists even better. Might "look" like Slices in Rust, Go and Zig but it's not.

let lista = [1..20]                      -- create a list from 1 to 20 of Integers

5 - List/For/Loop Comprehensions

Copied to Python and Scala. Killer feature, give a for-like super power expressions.

let result = [x*2 | x <- [1..10]]              -- creates a list because [] also numbers from 1 to 10 and multiply each by 2

boomBangs xs = [ if x < 10 then "BOOM!" else "BANG!" | x <- xs, odd x] -- here is a function we can use ifs too.

remove st = [ c | c <- st, c `elem` ['A'..'Z']]  -- here is a function to remove non upper case chars so we can do multiple computations there [] as you can see.

6 - We can do pattern matching with guards

Haskell has one of the best if the best pattern matcher in FP landscape.

factorial n
   | n < 2     = 1
   | otherwise = n * factorial (n - 1)

7 - Typeclasses

Haskell has relational algebra and is very veyr easy to create your own types and a very powerful type system for instace.

data SimplePerson = SimplePerson String String String Int String
    deriving Show

firstPerson :: SimplePerson
firstPerson = SimplePerson "John" "Doe" "jd@jd.com" 60 "Engineer"

Because we are diriving(extending) Show we can do print(since print calls show). Similarly like you would do with a Trait in Scala or Trait in Rust (all copied from here).

8 - Records

data PersonRecord = PersonRecord { first :: String
                     , last :: String
                     , age :: Int
                     , height :: Float
                     , phone :: String
                     , flavor :: String
                     } deriving (Show)

Haskell creates the functions to access the data for us here. Many languages have Recods like Scala, Java, Kotlin all copied from Haskell.

9 - Deriving

You can use deriving (Rust copy and called #[derive(Debug)]) and get a lot of capabilities like this. Eq: allows comparisons with (==), Read: Allow unmarshall from string, Bounded: can get mix, max bounds, Show: let you print. See we are not coding anything just via declarative forms telling what we want, yes we can orrivede if we need. This is like interfaces/iheritance in most of langs, but without sucking.

module Main where

data Day = Sunday | Monday | Tuesday | Wednesday | Thursday | Friday | Saturday 
           deriving (Eq, Ord, Show, Read, Bounded, Enum)

enumCanDoCoolStuff :: [Day]
enumCanDoCoolStuff = [Thursday .. Saturday]

main :: IO ()
main = do
    putStrLn "First day is: "
    print (minBound :: Day)
    putStrLn "Last day is: "
    print (maxBound :: Day)

    print enumCanDoCoolStuff

10. Datastructures - Stack

I know haskell can be scary: functors, applicatives, monoids, monads, reader monad, writter monad, state momand, etc... But let's look how hard is to create a stack datastructure in haskell, check this out.

newtype Stack a = Stack [a] deriving Show

empty = Stack []

push x (Stack xs)= Stack (x:xs)

pop (Stack []) = (Nothing, Stack [])
pop (Stack (x:xs)) = (Just x, Stack xs)

5 lines not bad right ? :-) OH but to use it must be very hard, check this out. Usage of the Stack:

main = do
    let stack = push 1 $ push 2 $ push 3 empty
    print stack

Haskell Resources

Other Tiny Essays

About me

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