Practical example of function currying in JS

partial_function_application.js

// I have some code that needs to use the following 
// construct repeatedly
for(i=0;i<classes.length;i++){
  var c = classes[i];
  for(j=0;j<centers.length;j++){
      var k = centers[k];

     // do something with [c,k], like,
     // demand[[c,k]] = expression;

  }
}

// The looping constructs are going to be duplicated 
// many times, so Im going to abstract it out

// abstraction for double nested loops              
var doubleListIterator = function(list1, list2, f){ 
  list1.forEach(function(c, i){                     
    list2.forEach(function(k, j){                   
      f(c,k,i,j);                                   
    });                                             
  });                                               
}                                                   

// now I can do this
doubleListIterator(['a', 'b', 'c'], [1,2,3], function(el1, el2){ 
  console.log(el1, el2);
}

// prints, 
// a 1
// b 2
// c 3

// great, but what if I want a double list iterator that always
// uses a certain 2 arguments (in my case 'classes' and 'centers',
// then we should curry this function to 'bind' the arguments
// so they dont need to be passed in explicitly each time

// simple currying function
var partial = function(f, list1, list2){   
  return function(nf){                     
    f(list1, list2, nf);                   
  }                                        
}                                          

// construct my special curried iterator
var ckIterator = partial(doubleListIterator, classes, centers);

// now instead of the super wordy thing up top, I can simply do,
ckIterator(function(c,k){

  // c, k here come from 'classes' and 'centers' 
  // and have been bound to this curried function

  // do something w/ c and k

});