Monoid factory

monoid-factory.js

'use strict';

var R = require('ramda');


var extract = R.invoke('extract', []);


var makeMonoid = R.curry(function(identity, binary, v) {

  // test monoid identity and binary here

  var thisMonoid    = makeMonoid(identity, binary);
  var curriedBinary = R.curry(binary);

  return {
    extract : R.always(v),
    empty   : R.partial(thisMonoid, identity),
    append  : R.compose(thisMonoid, curriedBinary(v), extract),
  };
});


function Monoid(props) {
  return makeMonoid(props.identity, props.binary);
}


function empty(m) {
  return m.empty ? m.empty() : m().empty();
}


function append(m1, m2) {
  return m1.append(m2);
}


function concat(ms) {
  return R.reduce(append, empty(R.head(ms)), ms);
}


var applyWith = R.curry(function(m, vs) {
  return extract(concat(R.map(m, vs)));
});


module.exports = {
  Monoid    : Monoid,
  empty     : empty,
  append    : append,
  concat    : concat,
  extract   : extract,
  applyWith : applyWith
};

usage_monoid-factory.js

'use strict';

var M = require('./monoid');

var Any = M.Monoid({
  identity: false,
  binary: function (v1, v2) {
    return v1 || v2;
  }
});


var Product = M.Monoid({
  identity: 1,
  binary: function (v1, v2) {
    return v1 * v2;
  }
});


// console.log(append(empty(Any), Any(true)).value);
//
// console.log(append(Any(false), Any.empty()).value);
//
// console.log(append(Any(false), Any(true)).value);
//
// console.log(append(Any(false), Any(false)).value);
//
console.log(M.concat([Any(false), Any(false), Any(true)]).extract());
console.log(M.concat([Any(false), Any(false), Any(false)]).extract());

var any = M.applyWith(Any);

console.log(any([false, false, true]));
console.log(any([false, false, false]));

console.log(M.applyWith(Product, [1, 3, 5, 8, 10]));