CODEWITHSUNDEEP
javascript
Mike K
Mike K

Reputation: 6521

How to properly curry with ES6?

Say I have,

const toUpperCase = word => word.toUpperCase();
const reverse = word => word.split('').reverse().join('')
const toLowerCase = word => word.toLowerCase();

How can I do something like,

const transformWord = word => toUpperCase(word) => reverse(word) => toLowerCase(word)
console.log(transformWord('abcdefg')) // expected output: gfedcba

Upvotes: 2

Views: 197

Answers (5)

Siva Kondapi Venkata
Siva Kondapi Venkata

Reputation: 11011

Use recursive approach to write curry function. Curry function returns a function if you pass the transform function and when you pass the word, it will all the transformations and return the result word. Only thing last has to be word.

transformWord(processA)(processB)(processN)(word)

const toUpperCase = word => word.toUpperCase();
const reverse = word => word.split('').reverse().join('')
const toLowerCase = word => word.toLowerCase();

const transformWord = arg => {
  const queue = [arg];

  const curry = item => {
    if (typeof item === "string") {
      let word = item;
      while (queue.length > 0) {
        const transform = queue.shift();
        word = transform(word);
      }
      return word;
    } else {
      queue.push(item);
      return curry;
    }
  };
  return curry;
};

console.log(transformWord(toUpperCase)(reverse)(toLowerCase)("abcdefg"));
console.log(transformWord(toUpperCase)("abcdefg"));

Upvotes: 0

Aravindan Venkatesan
Aravindan Venkatesan

Reputation: 628

const toUpperCase = word => word.toUpperCase();
const reverse = word => word.split('').reverse().join('')
const toLowerCase = word => word.toLowerCase();

const transformWord = word => toLowerCase(reverse(toUpperCase(word)));
console.log(transformWord('abcdefg')) //Output: gfedcba

Upvotes: 0

Bergi
Bergi

Reputation: 665564

I don't see what this has to do with currying. I think you're just looking for function composition:

const transformWord = word => toLowerCase(reverse(toUpperCase(word)))

Upvotes: 1

Nina Scholz
Nina Scholz

Reputation: 386883

You could take a pipe function which reduces the given function by using a parameter.

const
    pipe = (...functions) => input => functions.reduce((acc, fn) => fn(acc), input),
    toUpperCase = word => word.toUpperCase(),
    reverse = word => word.split('').reverse().join(''),
    toLowerCase = word => word.toLowerCase(),
    transformWord = pipe(toUpperCase, reverse, toLowerCase);


console.log(transformWord('abcdefg')) // expected output: gfedcba

Upvotes: 1

CertainPerformance
CertainPerformance

Reputation: 371233

You could use an array of the functions and reduce over them:

const toUpperCase = word => word.toUpperCase();
const reverse = word => word.split('').reverse().join('')
const toLowerCase = word => word.toLowerCase();

const transformWord = word => [toUpperCase, reverse, toLowerCase].reduce((lastVal, fn) => fn(lastVal), word);
console.log(transformWord('abcdefg')) // expected output: gfedcba

There's also the pipeline operator proposal which makes this look a whole lot neater, but that's ages away from being implemented (it's still stage 1):

const transformWord = word => word |> toUpperCase |> reverse |> toLowerCase;

Upvotes: 2

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