The Revision Object

gistfile1.js

var playFor = function(transformations,val) {
  return [val].concat(transformations.map(function(x){
    val = x[1](val);
    return val;
  }));
};

pop = function(arr) {
  return [arr.slice(0,1)[0],arr.slice(1,arr.length)];
}

compose2 = function(f1,f2) {
  return function(val){return f1(f2(val))};
}

compose = function(transformations) {  /*should get a reversed transHistory*/
  if (transformations.length === 1) {
    return function(x){return x};
  }
  var f = pop(transformations);
  return compose2(f[0],compose(f[1]));
}

var rev = function(value,History){
  return function(){
    var values;
    values =  History || [];
    if (value) values.push([value,function(){return value}]);
    
    var v = function(){
      if(values.length > 0) return values[values.length-1][0]
      return undefined
    }
    
    var history = function(b) {
        var length = values.length
        var back = (length > b ? b : length)
        return values.slice(length-back,length)
    }
      
    return {
      val : function(x) {
        if(x){
          values.push([x,function(){return x}]);
          return this;
        }
        else  return v();
      },
      trans : function(func) {
        if(func) {
          ret = func(v())
          values.push([ret,func]);
          return this;
        }
      },
      map : function(func) {
        if(func) {
          ret = v().map(func)
          values.push([ret, function(f) {return function(arr){return arr.map(f)}}(func)]);
          return this;
        }
      },
      allHistory : function(b) {
        return history(b);
      },
      valueHistory : function(b) {
        return history(b).map(function(value){
          return value[0];
        });
      },  
      transHistory : function(b) {
        return history(b).map(function(value){
          return value[1];
        });
      },
      spillGuts : function(){
        return rev(values.slice())
      },
      forwordFor : function(val) {
        return playFor(values.slice(1,values.length),val);
      },
      rewindFor : function(val) {
        return playFor(values.slice(1,values.length).reverse(),val)
      },      
      clone : function(){
        return rev(null,values.slice());
      },
      rollBack : function(){
        if (!values.length) throw Error("No History to Roll-In");
        return rev(null,values.slice(0,values.length-1));
      }
    }
  }()
}

var inc = function(x) {
  return x+1;
}

var incBy = function(x) {
  return function(y) {
    return x+y;
  }
}