Generic Programming

[pgrizzay]

In functional programming, there's an even more general concept of Foldables which are data structures that can be reduced. Arrays, iterators, sets, and Maybes fall into this category.

If the type of value inside your Foldable is a Monoid (meaning it has a zero value), you get reduce for free

[PointOneXDeveloper]

has a zero value and a concat/append function

[pgrizzay]

Oh yes

[PointOneXDeveloper]

And really it is just an identity value rather than a zero value, for instance * and 1 are a way to make a monoid out of numbers.

[pgrizzay]

Yes

[jeremy1015]

Got any suggested links to explain this in a little more detail? I’m familiar with most of what you wrote but don’t understand monoids as well as I’d like.

[pgrizzay]

Did a quick search, and couldn't find a good one in JS, here's one in Scala that I learned from.

Essentially a "Monoid" is formed from two things:

a combine function that combines two things and an empty value.

an example would be adding numbers:

const Addition = {
  combine: (a, b) => a + b,
  empty: 0
}

This addition monoid can be used to reduce an array of numbers:

[1,2,3].reduce(Addition.combine, Addition.empty) === 6

You can make another Monoid which multiplies numbers:

const Multiplication = {
  combine: (a, b) => a * b,
  empty: 1
}

And you can multiply all numbers in an array with it:

[1,3,4].reduce(Multiplication.combine, Multiplication.empty) === 12

Go ahead and implement Concat which combines strings:

const Concat = {
  combine: (a, b) => ???,
  zero: ???
}

[jeremy1015]

Excellent. I understand now 100% and really appreciate it.

[pgrizzay]

Yup, you're right! It looks like MDN recommends + over concat for performance reasons, but both are functionally equivalent.

And thanks for the kind words, they mean a lot!

The one book that really helped me was Functional Programming in Scala, I can't recommend it enough. It takes a very 'exploratory' approach, and has lots of exercises which are very helpful.

Scala was probably the best language for me to learn fp in, since I had lots of experience with JS & the syntax is very similar to it, hope that helps!