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Functional Programming Patterns With RamdaJS!

Fix the Flavors: Solution Review

Solution review.

We'll cover the following...

We know from the last exercise that lensPath is the easiest way to focus on everyone’s favorite flavor.

Javascript (babel-node)
import { lensPath } from 'ramda';
const favoriteFlavor = lensPath([
	'interests',
	'foods',
	'sweets',
	'iceCream',
	'favoriteFlavor'
]);

Then combining it with map and view will fetch them.

Javascript (babel-node)
import { lensPath, map, view } from 'ramda';
import employees from './employees.json';
const favoriteFlavor = lensPath([
	'interests',
	'foods',
	'sweets',
	'iceCream',
	'favoriteFlavor'
]);
const result = map(view(favoriteFlavor), employees);
console.log({ result });

But now there’s work to do in between. Before view, we need a setter lens. Unfortunately set is only good for static values.

Javascript (babel-node)
set(favoriteFlavor, 'Chocolate');

Uppercasing Flavors

over, however, lets us set using functions! We can use Ramda’s toUpper function to uppercase all the flavors.

Javascript (babel-node)
import { lensPath, map, over, toUpper, view } from 'ramda';
import employees from './employees.json';
const favoriteFlavor = lensPath([
	'interests',
	'foods',
	'sweets',
	'iceCream',
	'favoriteFlavor'
]);
const modifiedFlavors = map(over(favoriteFlavor, toUpper), employees);
const result = map(view(favoriteFlavor), modifiedFlavors);
console.log({ result });

Again, it’s a list of employees so map's necessary here. over focuses on an object using the favoriteFlavor lens, and uppercases its value.

That returns a new object with the modified flavors.

Passing that new array to map(view) returns the capitalized flavors.

Appending to Flavors

But wait there’s more! We must also append “IS A GREAT FLAVOR” to each of them.

We could combine that with toUpper using good ol’ pipe.

Javascript (babel-node)
import { lensPath, map, pipe, over, toUpper, view } from 'ramda';
import employees from './employees.json';
const favoriteFlavor = lensPath([
	'interests',
	'foods',
	'sweets',
	'iceCream',
	'favoriteFlavor'
]);
const modifiedFlavors = map(over(favoriteFlavor, pipe(toUpper, (flavor) => `${flavor} IS A GREAT FLAVOR`)), employees);
const result = map(view(favoriteFlavor), modifiedFlavors);
console.log({ result });

This does the job, but not very eloquently. Look at that nesting!

Javascript (babel-node)
const modifiedFlavors = map(over(favoriteFlavor, pipe(toUpper, (flavor) => `${flavor} IS A GREAT FLAVOR`)), employees);

Let’s create a helper function, emphasize.

Javascript (babel-node)
import { lensPath, map, pipe, over, toUpper, view } from 'ramda';
import employees from './employees.json';
const favoriteFlavor = lensPath([
	'interests',
	'foods',
	'sweets',
	'iceCream',
	'favoriteFlavor'
]);
const emphasize = pipe(
  toUpper,
  (flavor) => `${flavor} IS A GREAT FLAVOR`
);
const modifiedFlavors = map(over(favoriteFlavor, emphasize), employees);
const result = map(view(favoriteFlavor), modifiedFlavors);
console.log({ result });

Good, let’s go a step further.

Remember that lenses compose too. We don’t need to separate them and call map twice!

Javascript (babel-node)
import { lensPath, map, pipe, over, toUpper, view } from 'ramda';
import employees from './employees.json';
const favoriteFlavor = lensPath([
	'interests',
	'foods',
	'sweets',
	'iceCream',
	'favoriteFlavor'
]);
const emphasize = pipe(
  toUpper,
  (flavor) => `${flavor} IS A GREAT FLAVOR`
);
const emphasizeFlavor = pipe(
  over(favoriteFlavor, emphasize),
  view(favoriteFlavor)
);
const emphasizeFlavors = map(emphasizeFlavor);
const result = emphasizeFlavors(employees);
console.log({ result });