How to learn how to design your functions - Žygimantas Benetis

How to learn how to design
your functions
KaunasJS, Žygimantas Benetis <2018>

Outline
- Semantic design
- Monoids
- How to learn how to design your functions
- Programming languages and learning
- Summary

CV
Žygimantas Benetis
Software Engineer @ iGeolise <Scala, Frontend>
Coding since 2008
Studying data engineering/science

Code “design”
- What does it mean for code to be “good”?
- What does it mean for abstractions to not leak?

Code “design”
- To be composable?

Code “design”
- To be composable?
- Good code will let you build complex objects from simpler ones

Exercise: Define image (from Luke Palmer blog)
1. A rectangular array of colors (for a suitable definition of color);
2. A function taking a pair of real numbers and returning a possibly transparent
color;
3. A list of colored geometric primitives (polygons, lines, circles), where objects
later in the list are shown on top of objects earlier;
4. Any object with a draw method (our formalization of this very
software-oriented concept was a function from screens to screens)

Exercise: compose image
A straightforward composition operation on images is to put one on top of another.
Imagine what that would look like for each of the semantic domains:
1. The resulting image at coordinate (x,y) is an appropriate blend of the bottom
image at (x,y) and the top image at (x,y).
2. Same as above, except x and y are real numbers.
3. The resulting image is the bottom image concatenated with the top image.
4. The resulting image’s draw() method is { bottom.draw(); top.draw(); }.

Exercise: translate image
1. The pixel at (x,y) in the resulting image is a blend of the pixels around
(x-tx,y-ty) (if we can translate by non-integral amounts) if it is in the array’s
range. If not, it’s transparent. (Eliminate)
2. The resulting image at coordinate (x,y) is the original at coordinate (x+tx,
y+ty).
3. Translate each of the primitives in the list by (tx,ty).
4. Unclear how to define translation in this domain!
- It is not considered a bad start to start with const image = { draw: function() { } }
- Possible to extend with translate: function() {}
- Eliminate for not being as simple as possible

Exercise: image scaling
- For number 3 we need to consider what kind of primitive we have to scale
- For number 2 - its just (x, y) -> (x/s, y/s)

Summary for image exercise
- Function taking real numbers could doesn’t know about pixels
- Lots of “power” to library user
- Not always the best solution - sometimes restriction/less exposure is needed

Monoids
- Algebra which has identity element for specific associative operator
- Boolean: &&, true
- Addition: +, 0 {1 + 0 = 1, 10 + 0 = 10}
- Multiplication: *, 1 {7 * 1 = 7, 1337 * 1 = 1337}
- Associativity: {1 + 4 = 4 + 1, true && false = false && true}
- They are everywhere! (money summation, access rights to files, 2D shapes)

Monoids #2 from deque.blog
- Why them? They let you build complex behavior out of simple elements
without introducing new things
- Monoids can be chained indefinitely without introducing new types: 1+1+1+1..
- Associativity abstracts away the details of construction (1+1+3 != 1+3+1)
- Associativity lets you compute construction separately (parallel)
- If somebody else sees them - they will know how they behave
In JS: https://github.com/fantasyland/fantasy-land#monoid

How to learn to do better code design
- Using libraries without documentation [Less popular]
- Meaning of every word [Bentley]
- Relationships vs code [Linus and TinyLab]
- "Bad programmers worry about the code. Good programmers worry about data structures and
their relationships." - Linus Torvalds

Programming languages and learning
- Initial D
- Discovered vs Invented [Philip Wadler]
- Scala, Haskell, Elm, Clojure,...
- Javascript

Summary
- Thinking and considering semantic model before jumping into code
- Discovered is better than invented (abstract algebra and types)
- Choose tools which will teach you to be better

[AD] Looking for colleague to do frontend
● Decent HTML, CSS and Javascript experience
● Experience with functional programming or Scala
● Understanding of basic UI/UX design principles
● React knowledge is a huge plus
● Experience of working in Scrum/Agile environment is a plus
● Salary up to 42k per year

References
- https://deque.blog/2017/09/13/monoids-what-they-are-why-they-are-useful-an
d-what-they-teach-us-about-software/
- https://lukepalmer.wordpress.com/2008/07/18/semantic-design/
- Book I told you about -
https://www.manning.com/books/functional-and-reactive-domain-modeling

How to learn how to design your functions - Žygimantas Benetis

More Related Content

Similar to How to learn how to design your functions - Žygimantas Benetis (20)

Recently uploaded (20)

How to learn how to design your functions - Žygimantas Benetis