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<!DOCTYPE html>
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<title>Compare Procedures</title>
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<h1>SRFI 67: Compare Procedures</h1>
<p class="authors">by Sebastian Egner and Jens Axel Søgaard</p>
<p class="based-on"></p>
<p class="status">status: <em>final</em> (2005-09-11)</p>
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<li><a href="srfi-67.html">The SRFI Document</a></li>
<li><a href="https://srfi-email.schemers.org/srfi-67/">Discussion Archive</a></li>
<li><a href="https://github.com/scheme-requests-for-implementation/srfi-67">Git repo (on Github)</a></li>
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<h2>Abstract</h2> <p>This SRFI can be seen as an extension of the
standard procedures <code>=</code>, <code><</code>, <code>char<?</code> etc. of
R<sup>5</sup>RS -- or even as a replacement. The primary design aspect in
this SRFI is the separation of <em>representing</em> a total order and
<em>using it.</em> For representing the order, we have chosen for truly
3-way comparisons. For using it we provide an extensive set of
operations, each of which accepts a procedure used for comparison. Since
these compare procedures are often optional, comparing built-in types is
as convenient as R<sup>5</sup>RS , sometimes more convenient: For
example, testing if the integer index <em>i</em> lies in the integer
range {0, <code>...</code>, <em>n</em> <code>-</code> 1} can be written as
<code>(<=/<? 0 i n)</code>, implicitly invoking
<code>default-compare</code>.
<p>As soon as new total orders are required, the
infrastructure provided by this SRFI is far more convenient and often
even more efficient than building each total order from scratch.
<p>Moreover, in case Scheme users and implementors
find this mechanism useful and adopt it, the benefit of having a uniform
interface to total orders to be used in data structures will manifest
itself. Most concretely, a new sorting procedure in the spirit of this
SRFI would have the interface <code>(my-sort [ <i>compare</i> ]
<i>xs</i>)</code>, using <code>default-compare</code> if the optional
<i>compare</i> was not provided. Then <code>my-sort</code> could be defined
using the entire infrastructure of this SRFI: Efficient 2- and 3-way
branching, testing for chains and pairwise inequality, min/max, and
general order statistics.</body></html>