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Primitives for Expressing Iterative Lazy Algorithms
Extends the interpretation of a promise to include lazy and eager promises.
For more information see SRFI 45.
lazy[syntax] (lazy EXPRESSION) => promise
Returns a promise for EXPRESSION, which must evaluate to a SRFI 45 promise. (See lazy-strict.}
The promise will be iteratively forced, overwriting the promise at each step before the next iteration, so as to avoid storage leaks.
lazy-strict[procedure] (lazy-strict [STRICT?]) => boolean
The body EXPRESSION of a lazy promise must produce a result of type promise according to SRFI 45. This is the default behavior of this implementation. To accept a more lenient interpretation call with a value of #f for STRICT?.
The "improper use of `lazy'" error from force serves notice that a lazy expression was not of the correct type.
eager[syntax] (eager EXPRESSION) => promise
Returns a promise but immediately evaluates EXPRESSION.
force[procedure] (force PROMISE) => OBJECT
Returns the result of the evaluation of PROMISE. When PROMISE is an R5RS promise an R5RS force is performed and when PROMISE is not a promise it is the result.
delay[syntax] (delay EXPRESSION) => promise
Returns a SRFI-45 promise, a delayed evaluation of EXPRESSION.
lazy-promise?[procedure] (lazy-promise? OBJECT) => boolean
eager-promise?[procedure] (eager-promise? OBJECT) => boolean
recursive-promise?[procedure] (recursive-promise? OBJECT) => boolean
Is the OBJECT a recursive-promise; an eager or lazy promise?
promise?[procedure] (promise? OBJECT) => boolean
Some kind of promise? An R5RS promise or a recursive-promise.
(module foo (...) ; Allow access to the original API and stop those annoying ; redefined messages. (import (rename scheme (force r5rs:force) (delay r5rs:delay)) (rename chicken (promise? r5rs:promise?)) ...) (use srfi-45) ... code that can use R5RS and SRFI 45 promises ... )
- Supports multiple values for an eager promise and when (lazy-strict) is #f for a lazy promise.
- If compiled with the feature srfi-45-paranoia defined then extra sanity checks are enabled.
- The built-in routines are not rebound. This is purely a module implementation. As such the built-in promise? will not detect a recursive-promise as a promise. Do not allow these abstractions to leak into unsuspecting contexts.
- Added lazy-strict and compile-time feature srfi-45-paranoia. Better R5RS promise support by lazy.
- Redefines delay. Removed d-lay and recursive-delay.
- Bug fix for lazy R5RS promise in force. [Reported by Derrell Piper]
- Bug fix for too eager force. Removed "box" extension dependency.
- Chicken 4 release.
Copyright (C) 2009 Kon Lovett. All rights reserved.
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