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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.
The promise will be iteratively forced, overwriting the promise at each step before the next iteration, so as to avoid storage leaks.
eager[procedure] (eager EXPRESSION) => PROMISE
Returns a promise but immediately evaluates EXPRESSION.
Not much of a promise, more of a boxed value. For exposition purposes in algorithms.
delay[syntax] (delay EXPRESSION) => PROMISE
Returns a SRFI-45 promise, a delayed evaluation of EXPRESSION.
promise?[procedure] (promise? OBJECT) => BOOLEAN
Some kind of promise? An R5RS promise or a recursive promise.
recursive-promise?[procedure] (recursive-promise? OBJECT) => BOOLEAN
Recursive promise? A lazy or an eager promise.
lazy-promise?[procedure] (lazy-promise? OBJECT) => BOOLEAN
eager-promise?[procedure] (eager-promise? OBJECT) => BOOLEAN
force[procedure] (force PROMISE) => OBJECT
Returns the result of the evaluation of 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 ... )
Bugs and Limitations
- 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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