My yesterday night 1 hour code rush: JavaScript Hash with Range-based keys

hash_range.js

/**
 * September 20 night: 1 hour code rush
 * @FGRibreau
 * 
 * Requirements
 * ------------
 * The aim of this code rush is to enable developers to define a "range hash map" 
 * in a very expressive way (without if/then/else).
 *
 * Data-set
 * --------
 *
 * rules =
 *   Nb of days  ->  Precision levels set
 *  ---------------------------------------
 *  ] -∞ ; 1  ]  -> {min, hour, day, mon}
 *  ]  1 ; 8  ]  -> {hour, day, mon}
 *  ]  8 ; 62 ]  -> {day, mon}
 *  ] 62 ; +∞ [  -> {mon}
 *
 *
 * High-level API
 * --------------
 *
 * rules.getFor([days.number]) -> {}
 *
 * Note
 * ----
 *
 * - Only _.toArray() underscore method was used and it could easily be replaced by a Array::slice.call().
 * - The unit-tests use Qunit.
 */

var rules = new Rules()
    .add(range('] -∞ ; 1  ]'), precisions('min', 'hour', 'day', 'mon'))
    .add(range('] 1  ; 8  ]'), precisions('hour', 'day', 'mon'))
    .add(range('] 8  ; 62 ]'), precisions('day', 'mon'))
    .add(range('] 62 ; +∞ ['), precisions('mon'));

/**
 * Implementation
 */

function Rules(){
  var rules = [];
  this.add = function(range, value){
    if(!range.in){throw new Error("add(range, value), range must implement .in(Number) -> Boolean");}
    rules.push(_.toArray(arguments));
    return this;
  };

  this.getFor = function(n){
    var i = -1, iM = rules.length;
    while(i++ < iM){
      if(rules[i][0].in(n)){return rules[i][1];}
    }

    return undefined;
  };
};

function range(str){
  function car(s){return (s || '')[0];}
  function cdr(s){return (s || '').substring(1);}
  function cdl(s){return (s || '').substring(0, s.length-1);}
  function last(s){return (s || '')[s.length-1];}
  function toNumber(s){return s.indexOf('∞')>0 ? (s[0]==='-'?-1:1)/0 : parseInt(s, 10);}

  function _range(){
    var L, R, Lincluded, Rincluded;
    str = str.replace(/\s+/gi, '').split(';');

    this.Lincluded = Lincluded = car(str[0]) === '[';
    this.L         = L         = toNumber(cdr(str[0]));
    this.R         = R         = toNumber(cdl(str[1]));
    this.Rincluded = Rincluded = last(str[1]) === ']';

    this.in = function(n){
      return (
        (!Lincluded && n > L) || (Lincluded && n >= L)) && ((!Rincluded && n < R) || (Rincluded && n <= R)
      );
    };
  }

  return new _range();
};

function precisions(){return _.toArray(arguments);};

/**
 * Unit-tests
 */

// Test
function checkRangeParse(str, Lincluded, L, R, Rincluded){
  var _range = range(str);
  equal(_range.Lincluded, Lincluded, str + ' Lincluded =' + Lincluded);
  equal(_range.L, L, str + ' L =' + L);
  equal(_range.R, R, str + ' R =' + R);
  equal(_range.Rincluded, Rincluded, str + ' Rincluded =' + Rincluded);
}

checkRangeParse('] -∞ ; 1  ]', false, -Infinity, 1, true);
checkRangeParse('] 1  ; 8  ]', false, 1 , 8 , true);
checkRangeParse('] 8  ; 62 ]', false, 8 , 62, true);
checkRangeParse('] 62 ; +∞ [', false, 62, +Infinity, false);

// Test
function inRange(_range, _in, expected){
  equal(range(_range).in(_in), expected, _range + '.in('+_in+') = ' + expected);
}

inRange('] -∞ ; 1  ]', -10, true);
inRange('] -∞ ; 1  ]', 0, true);
inRange('] -∞ ; 1  ]', 1, true);
inRange('] -∞ ; 1  ]', 2, false);

inRange('] 1  ; 8  ]', 1, false);
inRange('] 1  ; 8  ]', 2, true);
inRange('] 1  ; 8  ]', 8, true);
inRange('] 1  ; 8  ]', 9, false);

inRange('] 8  ; 62 ]', 8, false);
inRange('] 8  ; 62 ]', 9, true);
inRange('] 8  ; 62 ]', 62, true);
inRange('] 8  ; 62 ]', 63, false);

inRange('] 62 ; +∞ [', 61, false);
inRange('] 62 ; +∞ [', 62, false);
inRange('] 62 ; +∞ [', 63, true);
inRange('] 62 ; +∞ [', 890, true);

// Test
function valueFor(_range, expected){
  deepEqual(rules.getFor(_range), expected, "rules.getFor("+_range+") " + JSON.stringify(expected));
}

valueFor(-1, ['min', 'hour', 'day', 'mon']);
valueFor(1, ['min', 'hour', 'day', 'mon']);
valueFor(2, ['hour', 'day', 'mon']);
valueFor(8, ['hour', 'day', 'mon']);
valueFor(9, ['day', 'mon']);
valueFor(62, ['day', 'mon']);
valueFor(63, ['mon']);
valueFor(6390, ['mon']);