monads-unwrapper.js

/*
* Monad is a container with some value and ability to perform mapping operation 
* on that value while returning result wrapped in a new Monad
*/

const Monad = value => ({
  // Return mapped (transformed via passed func) value
  flatMap: func => func(value),
  
  // Return mapped (transformed via passed func) value wrapped in new Monad 
  map (func) {;
    const newValue = this.flatMap(func);
    return Monad( newValue );
  },
  
  // For simple access
  value,
});

// ---------------------------------------------------------------------------------

// Example use:

// Utilities
const compose = (...fns) => x => fns.reduceRight((y, f) => f(y), x);
const map = func => mappable => mappable.map(func);
const trace = label => value => {
  console.log(`${ label }:`, value);
  return value;
};

// Create monad
const five = Monad(5)

// Define pipeline of composed functions
const inc = v => v + 1;
const double = v => v * 2;
const incThenDouble = compose(
  trace('Result'),
  double,
  inc
)

// Do something with monad
const result = five.map(incThenDouble); // Result: 12
console.log(result); // {flatMap: ƒ, map: ƒ, value: 12}

// Purpose of this all is still a mistery to me...