chickadee » srfi-45

srfi-45

Primitives for Expressing Iterative Lazy Algorithms

Documentation

Extends the interpretation of a promise to include lazy and eager promises.

For more information see SRFI 45.

lazy

(lazy EXPRESSION) -> promisesyntax

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

lazy-strict #!optional STRICT?parameter

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

(eager EXPRESSION) -> promisesyntax

Returns a promise but immediately evaluates EXPRESSION.

force

force PROMISEprocedure

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.

Note that force can produce a multi-valued return. See the Notes below,

delay

(delay EXPRESSION) -> promisesyntax

Returns a SRFI-45 promise, a delayed evaluation of EXPRESSION.

lazy-promise?

lazy-promise? OBJECTprocedure

eager-promise?

eager-promise? OBJECTprocedure

recursive-promise?

recursive-promise? OBJECTprocedure

Is the OBJECT a recursive-promise; an eager or lazy promise?

promise?

promise? OBJECTprocedure

Some kind of promise? An R5RS promise or a recursive-promise.

Usage

(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?))
    ...)
  (import srfi-45)
  ... code that can use R5RS and SRFI 45 promises ...
)

Notes

• 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.

Requirements

record-variants check-errors

Author

• André van Tonder
• Ported to Chicken 4 by Kon Lovett
• Ported to Chicken 5 by Sergey Goldgaber

Repository

This egg is hosted on the CHICKEN Subversion repository:

https://anonymous@code.call-cc.org/svn/chicken-eggs/release/5/srfi-45

If you want to check out the source code repository of this egg and you are not familiar with Subversion, see this page.

Version history

4.0.4

.

4.0.3

Fixed record printer.

4.0.2

Fixed types.

4.0.1

Fixed compiled test.

4.0.0 - Ported to Chicken 5

License

Copyright (C) 2009 Kon Lovett. All rights reserved.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the Software), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED ASIS, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.