#Underscore.loop

API

There are two functions to know:

1. loop( [ [ scope ], args ], fn )

   This function initiates a recursive loop. To enter the next iteration of the loop, use return this.loop( ...args ). Note that this.loop is a curried form of recurse described below, which means this.loop will occupy constant space in the stack. The arguments passed in to this.loop are passed in as arguments to the looping function.

2. recurse( fn, [ ...args ] )

   This function performs tail-call optimization on a recursive process. Note that this function call must be returned (in tail position) from your process for it to work. When the process is finished, simply return any value (except a call to recurse).

Example

Here is an implementation of the quicksort algorithm that demonstrates how these functions are used in practice:

function qsort(a, process) {
    if (a.length <= 1) return a;
    var pivot = _.first(a);
    if (!process) process = function (a, b) { return a <= b; };

    return _.loop( [ _.rest(a), [], [] ], function (a, less, greater) {
      if (_.isEmpty(a)) {
        return _.recurse(_.bind(qsort), less, process)
                .concat(pivot, _.recurse(_.bind(qsort), greater, process));
      } else {
        var first = _.first(a), l, g;
        if (process(first, pivot)) l = less.concat(first);
        else g = greater.concat(first);
        return this.loop(_.rest(a), l || less, g || greater);
      }
    });
  }