Monoid

Simple monoid factory in JavaScript. Compatible with the Fantasy Land JS Spec.

Easily define list reductions by providing an identity value and a binary function. Get a free way to reduce a list of monoids with concatAll.

Examples

Make a monoid and concat two monoid values.

var M = require('monoid');

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


// Use the monoid instance method
Any(true).append(Any(false));    // => Any(true)

// Or the free function provided by the Monoid module
M.append(Any(true), Any(false)); // => Any(true)

// Reduce an entire list of monoids
M.concatAll([Any(false), Any(false), Any(true)]);  // => Any(true)
M.concatAll([Any(false), Any(false), Any(false)]); // => Any(false)

Create a function to reduce a list of values using applyWith.

var any = M.applyWith(Any);

any([false, false, true]);  // => true
any([false, false, false]); // => true


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

M.applyWith(Product, [3, 5, 10]); // => 150

Note: M.applyWith(<Monoid>, list) is equivelent to M.extract(M.concatAll(list.map(<Monoid>))).

Use shorthand syntax for defining binaries. Currently available for +, *, || and &&.

var Sum = M.Monoid({
  identity : 0,
  binary   : '+'
});

var sum = M.applyWith(Sum);

sum([10, 32, 11]) // => 53

TODO

• More examples/docs
• Add more built in binaries
• Consider additional shorthand var Any = M.Monoid(false, '||').