E is an object-oriented programming language for secure distributed computing, created by Mark S. Miller, Dan Bornstein, Douglas Crockford, Chip Morningstar and others at Electric Communities in 1997. E is mainly descended from the concurrent language Joule and from Original-E, a set of extensions to Java for secure distributed programming. E combines message-based computation with Java-like syntax. A concurrency model based on event loops and promises ensures that deadlock can never occur. Philosophy The E language is designed for computer security and secure computing. This is performed mainly by strict adherence to the object-oriented computing model, which in its pure form, has properties that support secure computing. The E language and its standard library employ a capability-based design philosophy throughout in order to help programmers build secure software and to enable software components to co-operate even if they don't fully trust each other. In E, object references serve as capabilities, hence capabilities add no computational or conceptual overhead costs. The language syntax is designed to be easy for people to audit for security flaws. For example, lexical scoping limits the amount of code that must be examined for its effects on a given variable. As another example, the language uses the == operator for comparison and the := operator for assignment; to avoid the possibility of confusion, there is no = operator. Computational model In E, all values are objects and computation is performed by sending messages to objects. Each object belongs to a vat (analogous to a process). Each vat has a single thread of execution, a stack frame, and an event queue. Distributed programming is just a matter of sending messages to remote objects (objects in other vats). All communication with remote parties is encrypted by the E runtime. Arriving messages are placed into the vat's event queue; the vat's event loop processes the incoming messages one by one in order of arrival. E has two ways to send messages: an immediate call and an eventual send. An immediate call is just like a typical function or method call in a non-concurrent language: a sender waits until a receiver finishes and returns a value. An eventual send sends a message while producing a placeholder for a result called a promise. A sender proceeds immediately with the promise. Later, when a receiver finishes and yields a result, the promise resolves to a result. Since only eventual sends are allowed