ramda-examples.md

Ramda Examples

Ramda	Sometime Known As
all	every
always	const, constant
any	some
head	first, car
reduce	foldl
reduceRight	foldr
merge	extend, assign, mixin
zipObj	object, zipObject

Lift

const madd3 = R.lift(R.curry(function (a, b, c) {
  // [1, 1, 1]
  // [1, 2, 1]
  // [1, 3, 1]
  // [2, 1, 1]
  // [2, 2, 1]
  // [2, 3, 1]
  // [3, 1, 1]
  // [3, 2, 1]
  // [3, 3, 1]
  console.log(arguments);
  return a + b + c;
}));

madd3([1, 2, 3], [1, 2, 3], [1]); //=> [3, 4, 5, 4, 5, 6, 5, 6, 7]

composeK

R.composeK(h, g, f) == R.compose(R.chain(h), R.chain(g), R.chain(f))

//  parseJson :: String -> Maybe *
const parseJson = function (str) {
  try {
    str = JSON.parse(str);
  } catch (e) {
    // error
    return Maybe.Nothing();
  }
  return Maybe.of(str);
};

//  get :: String -> Object -> Maybe *
const get = function (str) {
  return R.compose(Maybe.of, R.prop(str));
};

//  getStateCode :: Maybe String -> Maybe String
var getStateCode = R.composeK(
  R.compose(Maybe.of, R.toUpper),
  get('state'),
  get('address'),
  get('user'),
  parseJson
);

getStateCode(Maybe.of('{"user":{"address":{"state":"ny"}}}')); // Just('NY')
getStateCode(Maybe.of('[Invalid JSON]')); // Nothing()

List Comprehension

/* 
 * Example:
 * Find any integer x, y, z that match the following conditions
 *   1. 0 < x < y < z < 10
 *   2. x * x + y * y = z * z
 * In Python:
 *  [(x,y,z) for x in range(1,10) for y in range(1,10) for z in range(1,10) if x < y and y < z and x * x + y * y == z * z]
 *  >>> [(3, 4, 5)]
 * In Javascript with Ramda:
 */ 
var R = require('ramda');
R.pipe(
  R.sequence(R.of), 
  R.filter(R.apply(function(x, y, z) { 
    return x < y && y < z && (x * x + y * y == z * z); 
  }))
)([R.range(1, 10), R.range(1, 10), R.range(1, 10)])
// [[3, 4, 5]]

Chain

const chain = R.curry(function (a, x) {
  let length = a.length;
  while (length > 0) x = a[--length](x);
  return x;
});

let foo = chain([map(inc), filter(odd), take(5)]);
foo([1,2,3,4,5,6,7,8,9,10]); // [2,4,6]
//or
chain([map(inc), filter(odd), take(5)], [1,2,3,4,5,6,7,8,9,10]); // [2,4,6]