/ramda-intro

Primary LanguageHTML

Ramda

--- ### What's Ramda

A Functional Programming Libraries in JavaScript

  • Designed in pure function style

  • Immutable structures

  • Functions are automatically curried

Purity

A function is pure if the return value is only determined by its input values,

and does not produce side effects.

const greet = (name) => 'Hello, ' + name

greet('Tracy') // 'Hello, Tracy'

Immutability

The function creates a copy of the structure instead of changes.

const arr1 =[1,2,3];

arr1.push(4);

arr1.push(5);

console.log(arr1); // [1, 2, 3, 4, 5]


var arr2 = [1, 2, 3];

console.log(R.append(4, arr2)); // [1, 2, 3, 4]

console.log(R.append(5, arr2)); // [1, 2, 3, 5]

Currying

A function with multiple arguments is transformed to a function with a single argument

returning another function with a single argument

const add = (a, b) => a + b;

const curriedAdd = (x) => (y) => x + y;

curriedAdd(10)(5) // 15

const add2 = curriedAdd(2) // (b) => 2 + b

add2(10) // 12

autoCurried

Why Curry

  • Function can be partially configure
  • Function are resue
const object = [{ id: 1 }, { id: 2 }, { id: 3 }];

object.map(function(o){
    return o.id;
});

const get = R.curry(function(property, object){
    return object[property];
});

object.map(get('id')) //= [1, 2, 3]

Installation

$ npm install ramda

import R from 'ramda';

or from a CDN

<script src="//cdnjs.cloudflare.com/ajax/libs/ramda/0.22.1/ramda.min.js"></script>

Type Signatures

Type Signatures (cont.)

  • Named Types: String, Number, Boolean ...

  • List of Values: [Number], [String] ...

  • Functions: (Number -> Number), (String -> [String]) ...

// findWords :: String -> [String]

const findWords = sentence => sentence.split(/\s+/);

findWords('She sells seashells by the seashore'); 

//=> ["She", "sells", "seashells", "by", "the", "seashore"]

Type Signatures (cont.)

  • Currying: Number → Number → Number
// calculateTax :: Number -> Number -> Number

const calculateTax = R.curry((rate,  base)
    => Math.round(100 * base + base * rate) / 100);
  • Type Variables : (a -> b) -> [a] -> [b]
// map :: (String -> Number) -> [String] -> [Number]
map(word => word.length, ['Four', 'score', 'and', 'seven']); 
//=> [4, 5, 3, 5]

// map :: (Number -> Number) -> [Number] -> [Number]
map(n => n * n, [1, 2, 3, 4, 5]); 
//=> [1, 4, 9, 16, 25]


// map :: (a -> b) -> [a] -> [b]

Let's buld a todo list

Todo list: list incomplete tasks

const incomplete = function(arr) {
  
  const tamp = [];
  
  arr.map((obj)=>{
    if(obj.complete === false){
      tamp.push(obj);
    }
  });
  
  return tamp;
}

console.log(incomplete(tasks));

Todo list: list incomplete tasks

const incomplete = function(arr) {
  
  const tamp = [];
  
  arr.map((obj)=>{
    if(obj.complete === false){
      tamp.push(obj);
    }
  });
  
  return tamp;
}

console.log(incomplete(tasks));

writing in ramda

const incomplete = R.filter(R.whereEq({complete: false}));

console.log(incomplete(tasks));

Todo list: list the tasks that active by user

const groupBy = function ( array , f ) {

  const groups = {};
  
  array.forEach((o)=>{
    const group = JSON.stringify(f(o));
    groups[group] = groups[group] || [];
    groups[group].push( o );  
  });
  
  return Object.keys(groups).map(( group )=>{
    return groups[group]; 
  })
}

console.log(groupBy(incomplete(tasks) , (obj) => [obj.username]));

Todo list: list the tasks that active by user

const groupBy = function ( array , f ) {

  const groups = {};
  
  array.forEach((o)=>{
    const group = JSON.stringify(f(o));
    groups[group] = groups[group] || [];
    groups[group].push( o );  
  });
  
  return Object.keys(groups).map(( group )=>{
    return groups[group]; 
  })
}

console.log(groupBy(incomplete(tasks) , (obj) => [obj.username]));

writing in ramda

const groupByUser = R.groupBy(R.prop('username'));
const activeByUser = R.compose(groupByUser, incomplete);

console.log(activeByUser(tasks));

DEMO

Todo List

Another Curry Example

--

Ref