brainstorms

Wednesday October 05, 2005

a proposal for r6rs [scheme] arithmetic

william clinger and michael sperber's preliminary proposal for r6rs arithmetic is a very good read for language implementors. [almost a textbook example of how to do these things]

This SRFI proposes to revise section 6.2 ("Numbers") of R5RS by:

• requiring a Scheme implementation to provide the full tower, including exact rationals of arbitrary precision, exact rectangular complex numbers with rational real and imaginary parts, and inexact real and complex arithmetic
• defining fixnum arithmetic (parameterized by precision)
• defining flonum arithmetic (inexactly)
• defining new procedures for performing exact arithmetic
• defining new procedures for performing inexact arithmetic
• describing the external representation and semantics of 0.0, -0.0, infinities and NaNs for systems that implement inexact real arithmetic using IEEE binary floating point
• changing the specification of eqv? to behave more sensibly with inexact numbers
• defining Scheme's real numbers to be the complex numbers whose imaginary part is an exact zero
• adding an external representation for inexact numbers that expresses the precision of a binary floating point representation
• defining procedures for some new operations, including integer division and bitwise operations remainder on real numbers,
• restricting the domains of some R5RS procedures
• clarifying the semantics of some R5RS procedures
• possibly changing the semantics of some R5RS procedures

there is a reference implementation in r5rs scheme.

related links:
scheme requests for implementations
r5rs [ps]

style and substance in patent licenses

adobe's tentative dng patent license:

Grant of Rights
Subject to the terms below and solely to permit the reading and writing of image files that comply with the DNG Specification, Adobe hereby grants all individuals and organizations the worldwide, royalty-free, non-transferable, non-exclusive right under all Essential Claims to make, have made, use, sell, import and distribute Compliant Implementations.

compare this to sun's non-assertion covenant for oasis open document format:

Sun irrevocably covenants that, subject solely to the reciprocity requirement described below, it will not seek to enforce any of its enforceable U.S. or foreign patents against any implementation of the Open Document Format for Office Applications (OpenDocument) v1.0 Specification, or of any subsequent version thereof ("OpenDocument Implementation") in which development Sun participates to the point of incurring an obligation, as defined by the rules of OASIS, to grant (or commit to grant) patent licenses or make equivalent non-assertion covenants.

[i was surprised to learn about the patent claims for the dng spec. down that road, i would have much preferred a no-nonsense, sun-style irrevocable covenant for dng.]