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*To*: srfi-33@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx*Subject*: bit vectors, exact integers, and sets*From*: Brad Lucier <lucier@xxxxxxxxxxxxxxx>*Date*: Wed, 24 Jul 2002 02:06:25 -0500 (EST)*Cc*: lucier@xxxxxxxxxxxxxxx*Delivered-to*: srfi-33@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

The SRFI says <excerpt> - This is a purely functional, side-effect-free implementation of bit operations -- all operations produce new, fresh results, rather than modifying old values. This can be implemented very efficiently for small bit vectors -- small enough to be unboxed values. Algorithms that work on larger bit vectors, however (such as data-flow analysis engines), might wish an alternate data-structure and associated set of operations that permits side-effecting or linear-updating operations (or both) on bit vectors. MIT Scheme, for example, provides such a facility. This should be considered for another SRFI. (See the short summary of the MIT Scheme system below.) I suggest that the design of such a system be deferred until SRFIs for strings and vectors have been finalised. Than a bit-vector SRFI could be designed that would preserve common structure with these other SRFIs, as well as the bitwise library in this SRFI. Note also that finite bit vectors have an isomorphism to finite sets. The design of both set-package and bit-vector SRFIs would probably want to keep this in mind -- maintaining parallel functional structure in the design. </excerpt> I don't think bit-vectors are that useful; you should stick with <excerpt> Bitstrings are represented by integers, using a two's-complement encoding of the bitstring. Thus every integer represents a semi-infinite bitstring, having either a finite number of zeroes (negative integers) or a finite number of ones (non-negative integers). </excerpt> Bitstrings represents sets of integers that are either finite or have finite complements. These seem to have very little to do with strings and vectors. Brad

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