Representing whiteboard diagrams as pure text while taking notes?

Question

I write all my notes in a simple text editor, and I have a hard time capturing diagrams, flowcharts, etc. as purely text. Do you know of any text-based shorthand for diagramming? Or have you developed your own techniques you wouldn't mind sharing?

An example might be:

UI - user clicks button
 |
TaskFactory - generates a Task based on user action and adds to TaskQueue
 |
TaskManager - checks for tasks on its own thread

Or maybe:

UI --> TaskFactory --> TaskQueue --> TaskManager --O

UI - user clicks button
TaskFactory - generates a Task based on user action
TaskQueue - Task is added to queue
TaskManager - on separate thread; processes tasks from the queue