Last week has been very immutable for me. I was looking into redux, Elm, React - just the ideas and trying to implement something similar for Angular.
For few years I have had a keen interest into functional programming and considered myself a good in the field. You know - using higher order functions, understand why
null is evil - so code produced by me was “fairly” functional. Avoiding state, writing functions as pure as possible. During the last year I upgraded my level to good novice by learning concepts of partials functions, functors. What is the next step? Tackle the real beast - learn the haskell. Baby steps.
Let’s start with Project Euler and go problem by problem googling haskell syntax and semantics on our way.
If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23. Find the sum of all the multiples of 3 or 5 below 1000.
Let’s go step by step.
- take first 1000 of natural numbers
- filter the list to only have multiples of
disibleByThreeOrFive n = if n `mod` 3 == 0 || n `mod` 5 == 0 then True else False
filter disibleByThreeOrFive [1..999]
which returns a list of all numbers we need to sum
- fold and sum them
haskell foldl (\res prev -> res + prev) 0 (filter disibleByThreeOrFive [1..999])which returns
233168. It is accepted by euler website - but the code we wrote could be improved.
First let’s get replace
sum (filter disibleByThreeOrFive [1..999])
Okay - those brackets are still there - good for us there is
$ operator which is exactly for that - getting rid of them. Anything that comes after dollar sign will take precedence.
sum $ filter disibleByThreeOrFive [1..999]
Making it a one liner by extracting to lambda function
sum $ filter (\x -> x `mod` 3 == 0 || x `mod` 5 == 0) [1..999]
Remembered a little bit of haskell syntax, tackled the new editor plugin change and looking forward to doing more exercises.
If you have any suggestions - I am eagerly waiting for feedback. https://benetis.me/old/posts/contact-me/