filter, reject, detect, some, every with error

1 files changed, 40 insertions, 31 deletions

diff --git a/README.md b/README.md
index 9cbf29e..b5a3664 100644
--- a/README.md
+++ b/README.md
@@ -34,7 +34,11 @@ async.map(['file1','file2','file3'], fs.stat, function(err, results){
     // results is now an array of stats for each file
 });
 
-async.filter(['file1','file2','file3'], fs.exists, function(results){
+async.filter(['file1','file2','file3'], function(filePath, callback) {
+  fs.access(filePath, function(err) {
+    callback(filepath, !err)
+  });
+}, function(err, results){
     // results now equals an array of the existing files
 });
 
@@ -395,25 +399,26 @@ __Related__
 __Alias:__ `select`
 
 Returns a new array of all the values in `arr` which pass an async truth test.
-_The callback for each `iteratee` call only accepts a single argument of `true` or
-`false`; it does not accept an error argument first!_ This is in-line with the
-way node libraries work with truth tests like `fs.exists`. This operation is
-performed in parallel, but the results array will be in the same order as the
-original.
+This operation is performed in parallel,
+but the results array will be in the same order as the original.
 
 __Arguments__
 
 * `arr` - An array to iterate over.
 * `iteratee(item, callback)` - A truth test to apply to each item in `arr`.
-  The `iteratee` is passed a `callback(truthValue)`, which must be called with a
+  The `iteratee` is passed a `callback(err, truthValue)`, which must be called with a
   boolean argument once it has completed.
-* `callback(results)` - *Optional* A callback which is called after all the `iteratee`
+* `callback(err, results)` - *Optional* A callback which is called after all the `iteratee`
   functions have finished.
 
 __Example__
 
 ```js
-async.filter(['file1','file2','file3'], fs.exists, function(results){
+async.filter(['file1','file2','file3'], function(filePath, callback) {
+  fs.access(filePath, function(err) {
+    callback(filepath, !err)
+  });
+}, function(err, results){
     // results now equals an array of the existing files
 });
 ```
@@ -502,17 +507,21 @@ __Arguments__
 
 * `arr` - An array to iterate over.
 * `iteratee(item, callback)` - A truth test to apply to each item in `arr`.
-  The iteratee is passed a `callback(truthValue)` which must be called with a
-  boolean argument once it has completed. **Note: this callback does not take an error as its first argument.**
-* `callback(result)` - *Optional* A callback which is called as soon as any iteratee returns
+  The iteratee is passed a `callback(err, truthValue)` which must be called with a
+  boolean argument once it has completed.
+* `callback(err, result)` - *Optional* A callback which is called as soon as any iteratee returns
   `true`, or after all the `iteratee` functions have finished. Result will be
   the first item in the array that passes the truth test (iteratee) or the
-  value `undefined` if none passed.  **Note: this callback does not take an error as its first argument.**
+  value `undefined` if none passed.
 
 __Example__
 
 ```js
-async.detect(['file1','file2','file3'], fs.exists, function(result){
+async.detect(['file1','file2','file3'], function(filePath, callback) {
+  fs.access(filePath, function(err) {
+    callback(filepath, !err)
+  });
+}, function(err, result){
     // result now equals the first file in the list that exists
 });
 ```
@@ -581,10 +590,7 @@ async.sortBy([1,9,3,5], function(x, callback){
 __Alias:__ `any`
 
 Returns `true` if at least one element in the `arr` satisfies an async test.
-_The callback for each iteratee call only accepts a single argument of `true` or
-`false`; it does not accept an error argument first!_ This is in-line with the
-way node libraries work with truth tests like `fs.exists`. Once any iteratee
-call returns `true`, the main `callback` is immediately called.
+If any iteratee call returns `true`, the main `callback` is immediately called.
 
 __Arguments__
 
@@ -592,15 +598,18 @@ __Arguments__
 * `iteratee(item, callback)` - A truth test to apply to each item in the array
   in parallel. The iteratee is passed a `callback(truthValue)`` which must be
   called with a boolean argument once it has completed.
-* `callback(result)` - *Optional* A callback which is called as soon as any iteratee returns
+* `callback(err, result)` - *Optional* A callback which is called as soon as any iteratee returns
   `true`, or after all the iteratee functions have finished. Result will be
   either `true` or `false` depending on the values of the async tests.
 
- **Note: the callbacks do not take an error as their first argument.**
 __Example__
 
 ```js
-async.some(['file1','file2','file3'], fs.exists, function(result){
+async.some(['file1','file2','file3'], function(filePath, callback) {
+  fs.access(filePath, function(err) {
+    callback(filepath, !err)
+  });
+}, function(err, result){
     // if result is true then at least one of the files exists
 });
 ```
@@ -617,26 +626,26 @@ __Related__
 __Alias:__ `all`
 
 Returns `true` if every element in `arr` satisfies an async test.
-_The callback for each `iteratee` call only accepts a single argument of `true` or
-`false`; it does not accept an error argument first!_ This is in-line with the
-way node libraries work with truth tests like `fs.exists`.
+If any iteratee call returns `false`, the main `callback` is immediately called.
 
 __Arguments__
 
 * `arr` - An array to iterate over.
 * `iteratee(item, callback)` - A truth test to apply to each item in the array
-  in parallel. The iteratee is passed a `callback(truthValue)` which must be
+  in parallel. The iteratee is passed a `callback(err, truthValue)` which must be
   called with a  boolean argument once it has completed.
-* `callback(result)` - *Optional* A callback which is called as soon as any iteratee returns
-  `false`, or after all the iteratee functions have finished. Result will be
-  either `true` or `false` depending on the values of the async tests.
-
- **Note: the callbacks do not take an error as their first argument.**
+* `callback(err, result)` - *Optional* A callback which is called after all the `iteratee`
+  functions have finished. Result will be either `true` or `false` depending on
+  the values of the async tests.
 
 __Example__
 
 ```js
-async.every(['file1','file2','file3'], fs.exists, function(result){
+async.every(['file1','file2','file3'], function(filePath, callback) {
+  fs.access(filePath, function(err) {
+    callback(filepath, !err)
+  });
+}, function(err, result){
     // if result is true then every file exists
 });
 ```