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<!--
SPDX-FileCopyrightText: 2013 John Cowan <[email protected]>
SPDX-License-Identifier: MIT
-->
<!DOCTYPE HTML PUBLIC "" "-//W3C//DTD HTML 3.2 Final//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<title>SRFI 113: Sets, Bags, Integer Sets, Enumeration Sets</title>
</head>
<body>
<H1>Title</H1>
Sets, bags, integer sets, enumeration sets
<H1>Author</H1>
John Cowan
<p>
This SRFI is currently in ``draft'' status.
To see an explanation of
each status that a SRFI can hold, see <a
href="http://srfi.schemers.org/srfi-process.html">here</a>.
To provide input on this SRFI, please
<a href="mailto:srfi minus 113 at srfi dot schemers dot org">mail to
<code><srfi minus 113 at srfi dot schemers dot org></code></a>. See
<a href="../../srfi-list-subscribe.html">instructions here</a> to
subscribe to the list. You can access previous messages via
<a href="mail-archive/maillist.html">the archive of the mailing list</a>.
</p>
<ul>
<li>Received: <a href="http://srfi.schemers.org/srfi-113/srfi-113-1.1.html">2013/05/31</a></li>
<li>Draft: 2013/06/01-2013/08/01</li>
</ul>
<H1>Abstract</H1><p><em>Sets</em> and <em>bags</em> (also known as multisets) are unordered mutable collections that can contain any Scheme object. Sets enforce the constraint that no two elements can be the same in the sense of the set's associated <em>equivalence procedure</em>; bags do not. <em>Integer sets</em> are a variant of sets that can only contain non-negative exact integers that are less than a maximum value specified when the integer set is created, and that always treat numerical equality as their equivalence procedure. <em>Enumeration sets</em> are another variant that can only contain symbols chosen from a set of symbols represented by an <em>enumeration type</em>; the equivalence procedure for them is <em>eq?</em>.
</p><H1>Issues</H1><ol><li>R6RS provides <tt>define-enumeration</tt> to help set up enum-types. Is this worth having? Possible syntax is:
<blockquote><p><tt>(define-enumeration </tt><type-name><tt> (</tt><symbol> ...<tt>)</tt> <constructor><tt>)</tt>
</p><p>
This would bind <tt><type-name></tt> to the enum-type, and <tt>constructor</tt> to a curried version of <tt>make-enum-set</tt> that already knows what type to use.
</p></blockquote></li><li><p>Should there be a mechanism to convert between integer sets and integers as bitvectors, as defined in SRFI 33, SRFI 60, and R6RS?</p></li><li><p>Currently you can convert one set type to another via lists. Are conversions directly through sets (or bags) useful enough to justify enlarging the SRFI? What about direct conversions between other types?</p></li><li><p>How about <tt>set-intern!</tt>, which is like <tt>set-value</tt> but adds the element to the set if it's not already there?</p></li></ol><H1>Rationale</H1><p>Sets are a standard part of the libraries of many high-level programming languages, including Smalltalk, Java, and C++. Although sets subsume integer sets and enumeration sets, providing them separately allows for increased implementation efficiency.</p><p>Insofar as possible, the names in this SRFI are harmonized with the names used for ordered collections (lists, strings, vectors, and bytevectors) in Scheme.</p><p>
The design of enumeration sets is founded on <a class="ext-link" href="http://www.r6rs.org/final/html/r6rs-lib/r6rs-lib-Z-H-15.html">R6RS enumerations</a>, but with the addition of reified enumeration types along the lines suggested by <a class="ext-link" href="http://www.r6rs.org/formal-comments/comment-262.txt"><span class="icon"></span>R6RS Formal Comment #262</a>. The prefix <tt>enum</tt> is used in all cases instead of using both <tt>enum</tt> and <tt>enumeration</tt> as R6RS does. Approximate mappings are shown below.
</p><H1>Specification</H1><p>The procedures in this SRFI are in the <code>(scheme sets)</code> and <code>(srfi xxx)</code> libraries (or <code>(srfi :xxx)</code> on R6RS). However, the sample implementation currently places them in the <code>(sets)</code> library instead.</p><p>
Sets, bags, integer sets, enumeration sets, and enumeration types are mutually disjoint, and disjoint from other types of Scheme objects.
</p><h2 id="Setprocedures">Set procedures</h2><p>
It is an error for a single procedure to be invoked on sets with different equivalence procedures.
</p><h3>Constructors</h3><p><tt>(make-set </tt><em>equivalence</em><tt>)</tt></p><p>
Returns a newly allocated empty set. <em>equivalence</em> is the equivalence procedure for the set. If it is coarser than <tt>equal</tt> (in the sense of R7RS-small 6.1), the implementation may signal an error; however, <tt>string-ci=?</tt> must be supported.
</p><p><tt>(set </tt><em>equivalence</em><tt> </tt><em>element</em><tt> ...)</tt></p><p>
Returns a newly allocated set with equivalence procedure <em>equivalence</em> and containing the <em>elements</em>.
</p><p><tt>(set-copy </tt><em>set</em><tt>)</tt></p><p>
Returns a newly allocated set containing the elements of <em>set</em>, with the same equivalence procedure.
</p><p><tt>(set-empty-copy </tt><em>set</em><tt>)</tt></p><p>
Returns a newly allocated set containing no elements with the same equivalence procedure as <em>set</em>.
</p><h3>Predicates</h3><p><tt>(set? </tt><em>obj</em><tt>)</tt></p><p>
Returns <tt>#t</tt> if <em>obj</em> is a set, and <tt>#f</tt> otherwise.
</p><p><tt>(set-member? </tt><em>set</em><tt> </tt><em>element</em><tt>)</tt></p><p>
Returns <tt>#t</tt> if <em>element</em> is a member of <em>set</em> and <tt>#f</tt> otherwise.
</p><h3>Mutators</h3><p><tt>(set-add! </tt><em>set</em><tt> </tt><em>element</em><tt>)</tt></p><p>
Adds <em>element</em> to <em>set</em> unless it is already a member. Returns an unspecified value.
</p><p><tt>(set-delete! </tt><em>set</em><tt> </tt><em>element</em><tt>)</tt></p><p>
Deletes <em>element</em> from <em>set</em> if it is a member. Returns <tt>#t</tt> if the element was a member, <tt>#f</tt> if not.
</p><h3>Mapping and folding</h3><p><tt>(set-map </tt><em>equivalence</em><tt> </tt><em>proc</em><tt> </tt><em>set</em><tt>)</tt></p><p>
Applies <em>proc</em> to each element of <em>set</em> in arbitrary order and returns a newly allocated set with the equivalence predicate <em>equivalence</em> which contains the results of the applications. For example:
<blockquote>
(set-map string-ci=? symbol->string (set eq? 'foo 'bar 'baz))
=> (set string-ci=? "foo" "bar" "baz")
</blockquote>
</p><p><tt>(set-for-each </tt><em>proc</em><tt> </tt><em>set</em><tt>)</tt></p><p>
Applies <em>proc</em> to <em>set</em> in arbitrary order, discarding the returned values. Returns unspecified results.
</p><p><tt>(set-fold </tt><em>proc</em><tt> </tt><em>nil</em><tt> </tt><em>set</em><tt>)</tt></p><p>
Invokes <em>proc</em> on each member of <em>set</em> in arbitrary order, passing the result of the previous invocation as a second argument. For the first invocation, <em>nil</em> is used as the second argument. Returns the result of the last invocation.
</p><p><tt>(set-unfold </tt><em>equivalence continue? mapper successor seed</em><code>)</code></p><p><p>Create a new set as if by <code>make-set</code>. If the result of applying the predicate <em>continue?</em> to <em>seed</em> is <code>#f</code>, return the set. Otherwise, apply the procedure <em>mapper</em> to <code>seed</code>. The value that <em>mapper</em> returns is added to the set. Then get a new seed by applying the procedure <em>successor</em> to <em>seed</em>, and repeat this algorithm.</p><h3>Conversion</h3><tt>(set->list </tt><em>set</em><tt>)</tt></p><p>
Returns a newly allocated list containing the members of <em>set</em> in unspecified order. However, repeated calls to this procedure will return a list in the same order until the set is mutated.
</p><p><tt>(list->set </tt><em>equivalence list</em><tt>)</tt></p><p>
Returns a newly allocated set with equivalence predicate <em>equivalence</em> containing the elements of <em>list</em>.
</p><h3>Subsets</h3><p><tt>(set=? </tt><em>set</em> ...<tt>)</tt>
</p><p>
Returns <tt>#t</tt> if each <em>set</em> contains the same elements.
</p><p><tt>(set<? </tt><em>set</em> ...<tt>)</tt>
</p><p>
Returns <tt>#t</tt> if each <em>set</em> other than the last is a proper subset of the following <em>set</em>, and <tt>#f</tt> otherwise.
</p><p><tt>(set>? </tt><em>set</em> ...<tt>)</tt>
</p><p>
Returns <tt>#t</tt> if each <em>set</em> other than the last is a proper superset of the following <em>set</em>, and <tt>#f</tt> otherwise.
</p><p><tt>(set<=? </tt><em>set</em> ...<tt>)</tt>
</p><p>
Returns <tt>#t</tt> if each <em>set</em> other than the last is a subset of the following <em>set</em>, and <tt>#f</tt> otherwise.
</p><p><tt>(set>=? </tt><em>set</em> ...<tt>)</tt>
</p><p>
Returns <tt>#t</tt> if each <em>set</em> other than the last is a superset of the following <em>set</em>, and <tt>#f</tt> otherwise.
</p><h3>The whole set</h3><p><tt>(set-size </tt><em>set</em><tt>)</tt></p><p>
Returns the number of elements in <em>set</em>.
</p><p><tt>(set-filter </tt><em>predicate</em><tt> </tt><em>set</em><tt>)</tt></p><p>
Returns a newly allocated set with the same equivalence predicate as <em>set</em> containing just the elements of <em>set</em> that satisfy <em>predicate</em>.
</p><p><tt>(set-remove </tt><em>predicate</em><tt> </tt><em>set</em><tt>)</tt></p><p>
Returns a newly allocated set with the same equivalence predicate as <em>set</em> containing just the elements of <em>set</em> that do not satisfy <em>predicate</em>.
</p><p><tt>(set-partition </tt><em>predicate</em><tt> </tt><em>set</em><tt>)</tt></p><p>
Returns two values, a newly allocated set with the same equivalence predicate as <em>set</em> containing just the elements of <em>set</em> that satisfy <em>predicate</em>, and another newly allocated set with the same equivalence predicate as <em>set</em> containing just the elements of <em>set</em> that do not satisfy <em>predicate</em>.
</p><p><tt>(set-count </tt><em>predicate</em><tt> </tt><em>set</em><tt>)</tt></p><p>
Returns the number of elements of <em>set</em> that satisfy <em>predicate</em> as an exact integer.
</p><p><tt>(set-find </tt><em>predicate</em><tt> </tt><em>set</em><tt>)</tt></p><p>
Returns an arbitrarily chosen element of <em>set</em> that satisfies <em>predicate</em>, or <code>#f</code> if there is none. Note the ambiguity: if you are searching for <code>#f</code>, you cannot tell if you have found it or not.
</p><p><tt>(set-any </tt><em>predicate</em><tt> </tt><em>set</em><tt>)</tt></p><p>
Returns <tt>#t</tt> if any element of <em>set</em> satisfies <em>predicate</em>, or <code>#f</code> otherwise.
</p><p><tt>(set-every </tt><em>predicate</em><tt> </tt><em>set</em><tt>)</tt></p><p>
Returns <tt>#t</tt> if every element of <em>set</em> satisfies <em>predicate</em>, or <code>#f</code> otherwise.
</p><h3>Set operations</h3><p><tt>(set-union </tt><em>set<sub>1</sub></em><tt> </tt><em>set<sub>2</sub></em> ...<tt>)</tt>
</p><p><tt>(set-intersection </tt><em>set<sub>1</sub></em><tt> </tt><em>set<sub>2</sub></em> ...<tt>)</tt>
</p><p><tt>(set-difference </tt><em>set<sub>1</sub></em><tt> </tt><em>set<sub>2</sub></em> ...<tt>)</tt>
</p><p><tt>(set-xor </tt><em>set<sub>1</sub></em><tt> </tt><em>set<sub>2</sub></em><tt>)</tt></p><p>
Returns a newly allocated set that is the union, intersection, asymmetric difference, or symmetric difference of the <em>sets</em>. Asymmetric difference is extended to more than two sets by taking the difference between the first set and the union of the others. Symmetric difference is not extended beyond two sets. Elements in the result set are drawn from the first set in which they appear.
</p><p><tt>(set-union! </tt><em>set<sub>1</sub></em><tt> </tt><em>set<sub>2</sub></em> ...<tt>)</tt>
</p><p><tt>(set-intersection! </tt><em>set<sub>1</sub></em><tt> </tt>set<sub>2</sub><em> ...<tt>)</tt>
</em></p><p><tt>(set-difference! </tt><em>set<sub>1</sub></em><tt> </tt><em>set<sub>2</sub></em> ...<tt>)</tt>
</p><p><tt>(set-xor! </tt><em>set<sub>1</sub></em><tt> </tt><em>set<sub>2</sub></em><tt>)</tt></p><p>
The same as <tt>set-union</tt>, <tt>set-intersection</tt>, <tt>set-difference</tt>, and <tt>set-xor</tt> respectively, but may mutate the <em>set<sub>1</sub></em> argument.
</p><h3>Set value</h3><p><tt>(set-value </tt><em>set</em><tt> </tt><em>element</em><tt>)</tt></p><p>
Returns the element of <em>set</em> that is equal, in the sense of the equivalence predicate, to <em>element</em>. If <em>element</em> is not a member of the set, it is returned.
</p><h2 id="Bagprocedures">Bag procedures</h2><p>
Bags are like sets, but can contain the same object more than once. However, if two elements that are equal in the sense of the equivalence procedure, but not in the sense of <code>eqv?</code>, are both included, it is not guaranteed that they will remain distinct when retrieved from the bag. It is an error for a single procedure to be invoked on bags with different equivalence procedures.
</p><p>
The procedures for creating and manipulating bags are the same as those for sets, except that <tt>set</tt> is replaced by <tt>bag</tt> in their names, and that adding an element to a bag is effective even if the bag already contains the element. There are no procedures <tt>bag-xor</tt>, <tt>bag-xor!</tt>, or <tt>bag-value</tt>.
</p><p><tt>(bag-element-count </tt><em>bag</em><tt> </tt><em>element</em><tt>)</tt></p><p>
Returns an exact integer representing the number of times that <em>element</em> appears in <em>bag</em>.
</p><p><tt>(bag-increment! </tt><em>bag<tt> </tt>element<tt> </tt>count</em><tt>)</tt></p><p><tt>(bag-decrement! </tt><em>bag<tt> </tt>element<tt> </tt>count</em><tt>)</tt></p><p>
Increases or decreases the element count of <em>element</em> in <em>bag</em> by the exact integer <em>count</em>.
</p><h2 id="Integersetprocedures">Integer set procedures</h2><p>
The elements of an integer set are non-negative exact integers less than the set's <em>limit</em>, which is specified when it is created. Except as noted below, the procedures for creating and manipulating integer sets are the same as those for sets, except that <tt>set</tt> is replaced by <tt>integer-set</tt> in their names, and references to equivalence predicates are replaced by limits, as the equivalence function is always <tt>=</tt>. Wherever a newly allocated integer set is returned, it has the same limit as the source sets. It is an error for a single procedure to be invoked on integer sets with different limits.
</p><p>
The procedure <tt>integer-set-value</tt> is just the identity function, so it is not provided.
</p><p><tt>(make-integer-set </tt><em>limit</em><tt>)</tt></p><p>
Returns a newly allocated integer set. The possible elements of the set are the exact integers from 0 to <em>limit</em> - 1, where <em>limit</em> is an exact non-negative integer. The set is empty.
</p><p><tt>(make-universal-integer-set </tt><em>limit</em><tt>)</tt></p><p>
Returns a newly allocated integer set. The possible elements of the set are the exact integers from 0 to <em>limit</em> - 1, where <em>limit</em> is an exact non-negative integer. The set contains all possible elements.
</p><p><tt>(integer-set-complement </tt><em>integer-set</em><tt>)</tt></p><p>
Returns a newly allocated integer set that is the complement of <em>integer-set</em>.
</p><p><tt>(integer-set-complement! </tt><em>integer-set</em><tt>)</tt></p><p>
Mutates <em>integer-set</em> to its complement.
</p><p><tt>(integer-set-min </tt><em>integer-set</em><tt>)</tt></p><p><tt>(integer-set-max </tt><em>integer-set</em><tt>)</tt></p><p>
Returns the smallest or largest integer in <i>integer-set</i>, or <tt>#f</tt> if there is none.
</p><p><tt>(integer-set-delete-min! </tt><em>integer-set</em><tt>)</tt></p><p><tt>(integer-set-delete-max! </tt><em>integer-set</em><tt>)</tt></p><p>
Returns and deletes the smallest or largest integer in <em>integer-set</em>, or <tt>#f</tt> if there is none.
</p><h2 id="Enumerationsets">Enumeration sets</h2><p>
Except as noted below, the procedures for creating and manipulating enumeration sets are the same as those for sets, except that <tt>set</tt> is replaced by <tt>enum-set</tt> in their names. Wherever a newly allocated enumeration set is returned, it has the same enumeration type as the source sets. It is an error for a single procedure to be invoked on enumeration sets with different enumeration types.
</p><p>
The procedure <tt>enum-set-value</tt> is just the identity function, so it is not provided.
</p><h3>Enum-type procedures</h3><p><tt>(make-enum-type </tt><em>enum-list</em><tt>)</tt></p><p>
Returns a newly allocated enumeration type suitable for constructing enumeration sets whose members are symbols. The elements of <em>enum-list</em> are either symbols or else pairs where the car is a symbol and the cdr is a distinct non-negative exact integer used to represent the symbol internally. If the element is a symbol, the implementation assigns its own choice of a distinct non-negative exact integer. These integers are called <em>indexes</em>. The symbols are said to be <em>in the enumeration type</em>. In R6RS the function of this procedure is provided as part of <tt>make-enumeration</tt>.
</p><p><tt>(enum-type-enums </tt><em>enum-type</em><tt>)</tt></p><p>
Return a newly allocated alist mapping the symbols in <em>enum-type</em> to their indexes.
</p><p><tt>(enum-type-index </tt><em>enum-type symbol</em><tt>)</tt></p><p>
Return the index of <em>symbol</em> in <em>enum-type</em>, or <tt>#f</tt> if it is not in <em>enum-type</em>. The R6RS equivalent is the procedure returned by <tt>enum-type-indexer</tt> when applied to an enum-set belonging to <tt>enum-type</tt>.
</p><p><tt>(enum-type-symbol </tt><em>enum-type index</em><tt>)</tt></p><p>
Returns the symbol whose index in <em>enum-type</em> is <em>index</em>, or <tt>#f</tt> if there is none.
</p><p><tt>(enum=? </tt><em>enum-type symbol</em> ...<tt>)</tt>
</p><p><tt>(enum<? </tt><em>enum-type symbol</em> ...<tt>)</tt>
</p><p><tt>(enum>? </tt><em>enum-type symbol</em> ...<tt>)</tt>
</p><p><tt>(enum<=? </tt><em>enum-type symbol</em> ...<tt>)</tt>
</p><p><tt>(enum>=? </tt><em>enum-type symbol</em> ...<tt>)</tt>
</p><p>
Returns <tt>#t</tt> if the indexes of the <em>symbols</em> are equal (which implies that the symbols themselves are <code>eq?</code>), monotonically increasing, monotonically decreasing, monotonically nondecreasing, and monotonically nonincreasing respectively, and <tt>#f</tt> otherwise.
</p><h3>Enum-set procedures</h3><p><tt>(make-enum-set </tt><em>enum-type</em><tt>)</tt></p><p>
Returns a newly allocated enumeration set. The possible elements of the set are the symbols in <em>enum-type</em>. The set is empty. The approximate R6RS equivalents are <tt>enum-set-constructor</tt> and <tt>make-enumeration</tt>.
</p><p><tt>(make-universal-enum-set </tt><em>enum-type</em><tt>)</tt></p><p>
Returns a newly allocated enumeration set. The possible elements of the set are the symbols in <em>enum-type</em>. The set contains all possible elements. The approximate R6RS equivalent is <tt>enum-set-universe</tt>.
</p><p><tt>(enum-set </tt><em>enum-type</em><tt> </tt><em>element</em> ...<tt>)</tt>
</p><p>
Returns a newly allocated enumeration set. The possible elements of the set are the symbols in <em>enum-type</em>. The set is initialized to contain the <em>elements</em>. There is no R6RS equivalent.
</p><p><tt>(list->enum-set </tt><em>enum-type</em><tt> </tt><em>list</em><tt>)</tt></p><p>
Returns a newly allocated enumeration set. The possible elements of the set are the symbols in <em>enum-type</em>. The set is initialized to contain the elements of <em>list</em>. There is no R6RS equivalent.
</p><p><tt>(enum-set-complement </tt><em>enum-set</em><tt>)</tt></p><p>
Returns a newly allocated enumeration set that is the complement of <em>enum-set</em>. This procedure is also in R6RS.
</p><p><tt>(enum-set-complement! </tt><em>enum-set</em><tt>)</tt></p><p>
Mutates <em>enum-set</em> to its complement. This procedure is also in R6RS.
</p><p><tt>(enum-set-min </tt><em>integer-set</em><tt>)</tt></p><p><tt>(enum-set-max </tt><em>integer-set</em><tt>)</tt></p><p>
Returns the smallest or largest symbol in symbol index order in <em>enum-set</em>, or <tt>#f</tt> if there is none.
</p><p><tt>(enum-set-delete-min! </tt><em>enum-set</em><tt>)</tt></p><p><tt>(enum-set-delete-max! </tt><em>enum-set</em><tt>)</tt></p><p>
Returns and deletes the smallest or largest symbol in symbol index order in <em>enum-set</em>, or <tt>#f</tt> if there is none.
</p><p><tt>(enum-set-projection </tt><em>enum-set</em><tt> </tt><em>enum-type</em><tt>)</tt></p><p>
Returns a newly allocated enumeration set of type <em>enum-type</em>. Its elements are the symbols belonging to <em>enum-set</em>, ignoring any symbols which are not in <em>enum-type</em>. This procedure is also in R6RS, but uses a second enum-set in place of <em>enum-type</em>.
</p><H1>Implementation</H1><p><b>Note: the present implementation does not yet support <tt>set-find</tt>, <tt>set-any</tt>, <tt>set-every</tt>, or the corresponding bag, integer set, and enum-set procedures.</b></p><p>Sets and bags are implemented as a thin veneer over hashtables, and integer sets over bytevectors. For clarity, the integer set implementation stores just one value into each bytevector element rather than the eight that would be possible. In turn, enumeration types are implemented over a hashtable from symbols to indexes, and enumeration sets over integer sets.</p><p>A sample implementation is <a href="sets.tar.gz">here</a>. The files <code>sets-impl.scm</code>, <code>bags-impl.scm</code>, <code>isets-impl.scm</code>, and <code>enums-impl.scm</code> are the basic code libraries for sets, bags, integer sets, and enumeration sets respectively. Each is divided into a section that makes use of the underlying collection and a section that doesn't. The file <code>count.scm</code> provides macros for conveniently looping over the bytevectors that underlie integer sets and enumeration sets. The file <code>srfi-4-shim.scm</code> is a minimal implementation of R7RS bytevectors on top of SRFI 4's u8vectors, just sufficient for this implementation, and may be useful for R5RS systems that do not provide R7RS bytevectors.</p><p>Two library definition files are provided: <code>sets.sld</code> provides an R7RS library named <code>(sets)</code> that exports the public procedures of this SRFI (the extension <code>.sld</code> is used by Chibi for library definition files). <code>sets.scm</code> is equivalent, but uses Chicken module syntax.</p><p>The file <code>sets-test.scm</code> is a test suite for this library. It uses Chicken's <code>test</code> egg, which is also provided on Chibi as an R7RS library named <code>(chibi test)</code>.</p>
<H1>Copyright</H1>
<p>Copyright (C) John Cowan 2013. All Rights Reserved.</p>
<p>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:</p>
<p>The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.</p>
<p>THE SOFTWARE IS PROVIDED "AS IS", 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.</p>
<hr />
<address>Editor: <a href="mailto:srfi-editors at srfi dot schemers dot org">
Mike Sperber</a></address>
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