monad.js

const curry = require('ramda').curry

var Monad = function(type, defs) {
    for (name in defs){
      type.prototype[name] = defs[name];
    }
    return type;
  };
  function Left(value){
    this.value = value
  }
  function Right(value){
    this.value=value;
  }
  
  Monad(Right, {
    bind:function(fn){
      return fn(this.value)
    }
  })
  
  Monad(Left, {
    bind: function(fn){
      return this;
    }
  })

  either = function(left, right, either){
    if(either.constructor.name === 'Right')
        return right(either.value)
    else
        return left(either.value)
}


var land = curry(function(lr, n, pole){
    pole[lr] = pole[lr] + n;
    if(Math.abs(pole[0]-pole[1]) > 3) {
      return new Left("dead when land " + n + " became " + pole);
    }
    return new Right(pole);
});

var landLeft = land(0)
var landRight = land(1);

var stillAlive = function(x){
    console.log(x)
}
var dead = function(x){
    console.log('皮尔斯' + x);
}

var walkInLine = new Right([0,0]);
eitherDeadOrNot = walkInLine.bind(landLeft(2)).bind(landRight(5))
either(dead, stillAlive, eitherDeadOrNot)
// => [2,5]
eitherDeadOrNot = walkInLine.bind(landLeft(2)).bind(landRight(5)).bind(landLeft(3)).bind(landLeft(10).bind(landRight(10)))

either(dead, stillAlive, eitherDeadOrNot)