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@@ -505,6 +505,46 @@ The `pick-out` consumer is interesting enough to see a quick example of:
(#\r #\e #\e #\r #\n)
```
+### Making New Generators
+
+Generators are subclasses of `gtwiwtg::generator!` that have at least
+two methods specialized on them:
+
+- `(gtwiwtg::next gen)` : advances the generator and its next value
+- `(gtwiwtg::nas-next-p gen)` : checks whether or not the generator has a next value
+
+Additionally, if your generator needs to perform cleanup after it is
+consumed, you can implement the `:after` method combination for the method
+
+- `(gtwiwtg::stop gen)` : is called by consumers to mark the generator
+ as stopped.
+
+None of the above are meant to be called by users of the library,
+which is why they are not exported symbols. But if you want to make
+your own generators you can.
+
+A silly example:
+
+``` lisp
+
+(defclass countdown (gtwiwtg::generator!)
+ ((value :reader countdown-value
+ :initarg :value
+ :initform 0)))
+
+(defmethod gtwiwtg::next ((g cowntdown))
+ (decf (countdown-value g)))
+
+(defmethod gtwiwtg::has-next-p ((g countdown))
+ (plusp (countdown-value g)))
+
+```
+
+You can see that `next` ASSUMES that there is a next value. This is
+one of the reasons you are not ment to call `next` manually. The
+`for` consumer automatcially checks that there is a next value before
+trying to get it.
+
## The Permutations Example
One final example to show you what you can do. Here is a function that