[JS Compose] 6. Semigroup examples

Posted 2020-08-23 Answer1215

Let‘s we want to combine two account accidently have the same name.

 

const acct1 = { name: ‘Nico‘, isPaid: true, points: 10, friends: [‘Franklin‘] }

const acct2 = { name: ‘Nico‘, isPaid: false, points: 2, friends: [‘Gatsby‘] }

 

So, here we can use Semi-group to combine them, because the semi-group have the knowledge how to combine for each type of object.

So we change two accounts as:

const acct1 = { name: First(‘Nico‘), isPaid: All(true), points: Sum(10), friends: [‘Franklin‘] }

const acct2 = { name: First(‘Nico‘), isPaid: All(false), points: Sum(2), friends: [‘Gatsby‘] }

 

But here we still have one problem which Object doesn‘t have ‘concat‘ method, so we need to use Immutable library to help:

Includes libarary:

const {Map} = Immutable;

const acct1 = Map({ name: First(‘Nico‘), isPaid: All(true), points: Sum(10), friends: [‘Franklin‘] })

const acct2 = Map({ name: First(‘Nico‘), isPaid: All(false), points: Sum(2), friends: [‘Gatsby‘] })

 

---------

const {Map} = Immutable;

const Sum = x =>
({
  x,
  concat: ({x: y}) =>
    Sum(x + y),
  inspect: () =>
    `Sum(${x})`
})

const All = x =>
({
  x,
  concat: ({x: y}) =>
    All(x && y),
  inspect: () =>
    `All(${x})`
})

const First = x =>
({
  x,
  concat: _ =>
    First(x),
  inspect: () =>
    `First(${x})`
})

const acct1 = Map({ name: First(‘Nico‘), isPaid: All(true), points: Sum(10), friends: [‘Franklin‘] })

const acct2 = Map({ name: First(‘Nico‘), isPaid: All(false), points: Sum(2), friends: [‘Gatsby‘] })

const res = acct1.concat(acct2)

// Showing results
console.log("Friend 1: ", res.toJS().friends[0]) //Friend 1: Franklin
console.log("Friend 2: ", res.toJS().friends[1]) //Friend 2: Gatsby
console.log("isPaid: ", res.toJS().isPaid.x) //isPaid: false
console.log("Name: ", res.toJS().name.x) // Name: Nico
console.log("Points: ", res.toJS().points.x) // Points: 12