Ramda Where Types

ramda_where_types.js

const { where, equals, gt, is, pipe, __, curry, tryCatch, either } = require('ramda');

const enforceType = curry((pred, obj) => {
  if (pred(obj)) return obj;
  throw new Error();
});

const catchTypeError = tryCatch(__, (err, obj) => void 0);

const gaurdedFn = (typePredicate, fn) => catchTypeError(
	pipe(enforceType(typePredicate), fn)
);

const userType = where({
  firstName: is(String),
  lastName: is(String),
  age: is(Number),
  sex: either(equals('M'), equals('F'))
});

const watchVideo = gaurdedFn(
  userType,
  curry((user, website) => Object.assign({}, user, { video: website }))
);

const isAdult = where({ age: gt(__, 18) });

const watchAdultVideo = gaurdedFn(
  pipe(enforceType(userType), enforceType(isAdult)),
  curry((user, website) => Object.assign({}, user, { adultVideo: website }))
);

const renameUser = gaurdedFn(
  userType,
  curry((user, firstName, lastName) => Object.assign({}, user, {firstName, lastName}))
);

const User = function(user) {
	enforceType(userType, user);
	this.firstName = user.firstName;
	this.lastName = user.lastName;
	this.sex = user.sex;
	this.age = user.age;
	this.rename = renameUser(this);
	this.watchVideo = watchVideo(this);
	this.watchAdultVideo = watchAdultVideo(this);
}

const assert = (isTrue, msg) => { if (!isTrue) throw new Error(msg)};
const isNamedFizzbuzz = enforceType(where({ firstName: equals('fizz'), lastName: equals('buzz') }))
const isNamedFooBar = enforceType(where({ firstName: equals('foo'), lastName: equals('bar') }))

let adult = new User({firstName: 'foo', lastName: 'bar', age: 20, sex: 'F'});
assert(isNamedFooBar(adult), 'Should get default names');
adult = adult.rename("fizz", "buzz")
assert(isNamedFizzbuzz(adult), 'Should rename properly');
console.log(adult.watchVideo("youtube"));
console.log(adult.watchAdultVideo("pornhub"));

const child = new User({firstName: 'foo', lastName: 'bar', age: 11, sex: 'F'});
console.log(child.rename("fizz", "buzz"));
console.log(child.watchVideo("youtube"));

console.log([
{firstName: 'billy', lastName: 'bob', age: 11, sex: 'F'},
{firstName: 'foo', lastName: 'bar', age: 17, sex: 'F'},
{firstName: 'foo', lastName: 'bar', age: 18, sex: 'F'},
{firstName: 'foo', lastName: 'bar', age: 19, sex: 'F'},
{firstName: 'foo', lastName: 'bar', age: 99, sex: 'F'}
].map(watchVideo).map(fn => fn('youtube.com')));

console.log([
{firstName: 'billy', lastName: 'bob', age: 11, sex: 'F'},
{firstName: 'foo', lastName: 'bar', age: 17, sex: 'F'},
{firstName: 'foo', lastName: 'bar', age: 18, sex: 'F'},
{firstName: 'foo', lastName: 'bar', age: 19, sex: 'F'},
{firstName: 'foo', lastName: 'bar', age: 99, sex: 'F'}
].map(watchAdultVideo).map(fn => fn && fn('pornhub.com')));