1. 6
    Create types with Semigroups
    5m 52s

Create types with Semigroups

Brian Lonsdorf
InstructorBrian Lonsdorf

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An introduction to concatting items via the formal Semi-group interface. Semi-groups are simply a type with a concat method that are associative. We define three semigroup instances and see them in action.

Benji Shine
Benji Shine
~ 3 years ago

Can you explain the {x: y} in the parameter to concat?

concat: ({x: y}) =>
    Sum(x + y),

Is that the same x as on the line above it?

Benji Shine
Benji Shine
~ 3 years ago

I think I understand, now that I've read the transcript:

I like to destructure this other Sum so why don't we say x and we'll assign it to y, and now we can just say x + y, much simpler. We are destructuring Sum type and just grabbing x off of it and calling it a y here. It should still work, and there we have it.

In the statement lots = Sum(3).concat(50) , the destructuring assignment makes the values be...

concat({x:  y}) => {
  // x is 3 and y is 50
  return Sum(3 + 50);

This is just like saying:

 const { x: y } = { x: 50 }; 
// now y = 50