Event-driven programming

Tcl is designed to use an event-driven model. This means that everything that should happen is either scheduled for a particular time or when an event occurs, such as data being read, a new connection is made, or an external application or database sends a notification. This means that your files, networking, and timers work in the same thread and use events to perform actions when something occurs. For example, in an application with user interface, an action can be bound to user clicking on a button, which causes specific code to be run whenever the user clicks on the button. Similarly, a network server will set up a listening connection and run specific code when a new connection is established. Similarly, whenever application can read or write to a network connection, the particular code can be run.

It is common to develop an application that is event driven. This means that in most cases the application will only do things when an event takes place or will perform...