Lazyevaluated

Lazyevaluated is a term used to describe an expression or computation whose evaluation is deferred until its value is required. It denotes a non-strict evaluation strategy in which expressions are not immediately reduced to values, allowing potentially infinite data structures and avoidance of unnecessary work.

In theory and practice, lazy evaluation is often implemented through thunks—delayed computations that are evaluated at most once when their result is needed. When a value is demanded, the runtime evaluates the thunk and caches the result (call-by-need). If the result is requested again, the cached value is reused, preventing repeated work. This contrasts with eager or strict evaluation, where expressions are evaluated as soon as they are bound.

Languages differ in their default or optional use of laziness. Haskell is the most well-known language with lazy evaluation by default, enabling powerful abstractions and infinite lists. Other languages support lazy features to varying degrees: OCaml has a lazy keyword, Scheme and Racket offer lazy constructs and streams, Clojure provides lazy sequences, and Python and JavaScript offer generators or similar facilities to implement laziness.

Benefits of lazyevaluated semantics include the ability to represent and manipulate infinite data structures, improved performance by skipping unnecessary computations, and modular control over evaluation order. Drawbacks include potential space leaks from unevaluated thunks, complexity in reasoning about performance, and complications when side effects or I/O are involved, as laziness can defer effects until evaluation occurs.

Overall, lazyevaluated describes an approach where computation is postponed until needed, trading determinism of timing for potential efficiency and expressive power.