Engine (computer science)

An engine is a continuation-based construct that provides timed preemption. Engines which can contain other engines are sometimes called Nesters^[1] and engines which do not have this ability are then called flat engines or "solo engines". To implement timed preemption there needs to be a clock. This clock can measure real time or simulated time. Simulated time can be implemented in a language like Scheme, by making each function start with decrementing the clock.^[2]

  (define-syntax timed-lambda
    ((_ formals exp1 exp2 ...)
      (lambda formals (decrement-timer) exp1 exp2 ...))))