An example of currying and partial application

currying.js

// Manual currying (no abstraction; right to left)

function prop(key) {
  return function (object) {
    return object[key]
  };
}

var nameProp = prop('name');
[ { name: 'Bob' } ].map(nameProp);


// Currying (right to left)

function curry2(fun) {
  return function(arg2) {
    return function(arg1) {
      return fun(arg1, arg2);
    };
  };
}

function prop(object, key) {
  return object[key]
}

var nameProp = curry2(prop)('name');
[ { name: 'Bob' } ].map(nameProp);

partial-application.js

// Manual partial application (no abstraction; right to left)

function prop(key) {
  return function () {
    var object = arguments[0];
    return object[key];
  };
}

var nameProp = prop('name');
[ { name: 'Bob' } ].map(nameProp);


// Partial application (left to right)

// This will only work when the partial application is done from the leftmost argument,
// because the map function will receive additional unwanted arguments. Thus, I have
// been forced to change the order of parameters inside of my `prop` function.

function prop(key, object) {
  return object[key]
}

var nameProp = _.partial(prop, 'name');
[ { name: 'Bob' } ].map(nameProp);


// Partial application (right to left) with currying (right to left)

function curry(fun) {
  return function(arg) {
    return fun(arg);
  };
}

function prop(object, key) {
  return object[key]
}

// We need to curry our partially applied function, because `map` provides unwanted arguments
var nameProp = curry(_.partialRight(prop, 'name'));
[ { name: 'Bob' } ].map(nameProp);