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Fantas, Eel, and Specification
const { tagged } = require('daggy')
const First = tagged('val')
First.prototype.concat = function (that) {
return this
}
const Min = tagged('val')
Min.prototype.concat = function (that) {
return Min(Math.min(this.val, that.val))
}
const Any = tagged('val')
Any.prototype.concat = function (that) {
return Any(this.val || that.val)
}
const Tuple4 = tagged('a', 'b', 'c', 'd')
Tuple4.prototype.concat = function (that) {
return Tuple4(this.a.concat(that.a),
this.b.concat(that.b),
this.c.concat(that.c),
this.d.concat(that.d))
}
const Customer = tagged(
'name',
'favouriteThings',
'registrationDate',
'hasMadePurchase'
)
const myStrategy = {
to: customer => Tuple4(
First(customer.name),
customer.favouriteThings,
Min(customer.registrationDate),
Any(customer.hasMadePurchase)
),
from: ({ a, b, c, d }) =>
Customer(a.val, b, c.val, d.val)
}
const merge = strategy => x => y =>
strategy.from(
strategy.to(x)
.concat(strategy.to(y))
)
const Tom1 = Customer('Tom', ['socks'], 100000, false)
const Tom2 = Customer('TomH', ['gloves'], 90000, true)
// { name: 'Tom'
// , favouriteThings: ['socks', 'gloves']
// , registrationDate: 90000
// , hasMadePurchase: true
// }
merge(myStrategy)(Tom1)(Tom2)
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