Dememoised get-neighbours, as the optimisation only works in deep

recursion which I'm no longer doing.

LICENSE

@@ -1,258 +1,340 @@
-# GNU GENERAL PUBLIC LICENSE
+GNU GENERAL PUBLIC LICENSE
+                       Version 2, June 1991
 
-Version 2, June 1991
+ Copyright (C) 1989, 1991 Free Software Foundation, Inc., <http://fsf.org/>
+ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
 
-Copyright (C) 1989, 1991 Free Software Foundation, Inc.  
+                            Preamble
-51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
 
-Everyone is permitted to copy and distribute verbatim copies
+  The licenses for most software are designed to take away your
-of this license document, but changing it is not allowed.
+freedom to share and change it.  By contrast, the GNU General Public
-Preamble
+License is intended to guarantee your freedom to share and change free
+software--to make sure the software is free for all its users.  This
+General Public License applies to most of the Free Software
+Foundation's software and to any other program whose authors commit to
+using it.  (Some other Free Software Foundation software is covered by
+the GNU Lesser General Public License instead.)  You can apply it to
+your programs, too.
 
-The licenses for most software are designed to take away your freedom to share 
+  When we speak of free software, we are referring to freedom, not
-and change it. By contrast, the GNU General Public License is intended to guarantee 
+price.  Our General Public Licenses are designed to make sure that you
-your freedom to share and change free software--to make sure the software is free 
+have the freedom to distribute copies of free software (and charge for
-for all its users. This General Public License applies to most of the Free 
+this service if you wish), that you receive source code or can get it
-Software Foundation's software and to any other program whose authors commit to 
+if you want it, that you can change the software or use pieces of it
-using it. (Some other Free Software Foundation software is covered by the GNU 
+in new free programs; and that you know you can do these things.
-Lesser General Public License instead.) You can apply it to your programs, too.
 
-When we speak of free software, we are referring to freedom, not price. Our 
+  To protect your rights, we need to make restrictions that forbid
-General Public Licenses are designed to make sure that you have the freedom to 
+anyone to deny you these rights or to ask you to surrender the rights.
-distribute copies of free software (and charge for this service if you wish), 
+These restrictions translate to certain responsibilities for you if you
-that you receive source code or can get it if you want it, that you can change 
+distribute copies of the software, or if you modify it.
-the software or use pieces of it in new free programs; and that you know you 
-can do these things.
 
-To protect your rights, we need to make restrictions that forbid anyone to 
+  For example, if you distribute copies of such a program, whether
-deny you these rights or to ask you to surrender the rights. These restrictions 
+gratis or for a fee, you must give the recipients all the rights that
-translate to certain responsibilities for you if you distribute copies of the 
+you have.  You must make sure that they, too, receive or can get the
-software, or if you modify it.
+source code.  And you must show them these terms so they know their
+rights.
 
-For example, if you distribute copies of such a program, whether gratis or for 
+  We protect your rights with two steps: (1) copyright the software, and
-a fee, you must give the recipients all the rights that you have. You must make 
+(2) offer you this license which gives you legal permission to copy,
-sure that they, too, receive or can get the source code. And you must show them 
+distribute and/or modify the software.
-these terms so they know their rights.
 
-We protect your rights with two steps: (1) copyright the software, and (2) 
+  Also, for each author's protection and ours, we want to make certain
-offer you this license which gives you legal permission to copy, distribute 
+that everyone understands that there is no warranty for this free
-and/or modify the software.
+software.  If the software is modified by someone else and passed on, we
+want its recipients to know that what they have is not the original, so
+that any problems introduced by others will not reflect on the original
+authors' reputations.
 
-Also, for each author's protection and ours, we want to make certain that 
+  Finally, any free program is threatened constantly by software
-everyone understands that there is no warranty for this free software. If the 
+patents.  We wish to avoid the danger that redistributors of a free
-software is modified by someone else and passed on, we want its recipients to 
+program will individually obtain patent licenses, in effect making the
-know that what they have is not the original, so that any problems introduced 
+program proprietary.  To prevent this, we have made it clear that any
-by others will not reflect on the original authors' reputations.
+patent must be licensed for everyone's free use or not licensed at all.
 
-Finally, any free program is threatened constantly by software patents. We wish 
+  The precise terms and conditions for copying, distribution and
-to avoid the danger that redistributors of a free program will individually 
+modification follow.
-obtain patent licenses, in effect making the program proprietary. To prevent 
-this, we have made it clear that any patent must be licensed for everyone's 
-free use or not licensed at all.
 
-The precise terms and conditions for copying, distribution and modification follow.
+                    GNU GENERAL PUBLIC LICENSE
+   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
 
-## TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
+  0. This License applies to any program or other work which contains
+a notice placed by the copyright holder saying it may be distributed
+under the terms of this General Public License.  The "Program", below,
+refers to any such program or work, and a "work based on the Program"
+means either the Program or any derivative work under copyright law:
+that is to say, a work containing the Program or a portion of it,
+either verbatim or with modifications and/or translated into another
+language.  (Hereinafter, translation is included without limitation in
+the term "modification".)  Each licensee is addressed as "you".
 
-0. 	This License applies to any program or other work which contains a notice 
+Activities other than copying, distribution and modification are not
-	placed by the copyright holder saying it may be distributed under the terms of 
+covered by this License; they are outside its scope.  The act of
-	this General Public License. The "Program", below, refers to any such program 
+running the Program is not restricted, and the output from the Program
-	or work, and a "work based on the Program" means either the Program or any 
+is covered only if its contents constitute a work based on the
-	derivative work under copyright law: that is to say, a work containing the 
+Program (independent of having been made by running the Program).
-	Program or a portion of it, either verbatim or with modifications and/or 
+Whether that is true depends on what the Program does.
-	translated into another language. (Hereinafter, translation is included without 
-	limitation in the term "modification".) Each licensee is addressed as "you".
-	
-	Activities other than copying, distribution and modification are not covered by 
-	this License; they are outside its scope. The act of running the Program is not 
-	restricted, and the output from the Program is covered only if its contents 
-	constitute a work based on the Program (independent of having been made by 
-	running the Program). Whether that is true depends on what the Program does.
 
-1. 	You may copy and distribute verbatim copies of the Program's source code as 
+  1. You may copy and distribute verbatim copies of the Program's
-	you receive it, in any medium, provided that you conspicuously and appropriately 
+source code as you receive it, in any medium, provided that you
-	publish on each copy an appropriate copyright notice and disclaimer of warranty; 
+conspicuously and appropriately publish on each copy an appropriate
-	keep intact all the notices that refer to this License and to the absence of any 
+copyright notice and disclaimer of warranty; keep intact all the
-	warranty; and give any other recipients of the Program a copy of this License 
+notices that refer to this License and to the absence of any warranty;
-	along with the Program.
+and give any other recipients of the Program a copy of this License
-	
+along with the Program.
-	You may charge a fee for the physical act of transferring a copy, and you may at 
-	your option offer warranty protection in exchange for a fee.
-	
-2. 	You may modify your copy or copies of the Program or any portion of it, thus 
-	forming a work based on the Program, and copy and distribute such modifications 
-	or work under the terms of Section 1 above, provided that you also meet all of 
-	these conditions:
-	
-	a) You must cause the modified files to carry prominent notices stating that 
-	   you changed the files and the date of any change.
-	b) You must cause any work that you distribute or publish, that in whole or in 
-	   part contains or is derived from the Program or any part thereof, to be 
-	   licensed as a whole at no charge to all third parties under the terms of this 
-	   License.
-	c) If the modified program normally reads commands interactively when run, you
-	   must cause it, when started running for such interactive use in the most 
-	   ordinary way, to print or display an announcement including an appropriate 
-	   copyright notice and a notice that there is no warranty (or else, saying 
-	   that you provide a warranty) and that users may redistribute the program 
-	   under these conditions, and telling the user how to view a copy of this 
-	   License. (Exception: if the Program itself is interactive but does not 
-	   normally print such an announcement, your work based on the Program is not 
-	   required to print an announcement.)
-	   
-	These requirements apply to the modified work as a whole. If identifiable 
-	sections of that work are not derived from the Program, and can be reasonably 
-	considered independent and separate works in themselves, then this License, 
-	and its terms, do not apply to those sections when you distribute them as 
-	separate works. But when you distribute the same sections as part of a whole 
-	which is a work based on the Program, the distribution of the whole must be on 
-	the terms of this License, whose permissions for other licensees extend to the 
-	entire whole, and thus to each and every part regardless of who wrote it.
-	
-	Thus, it is not the intent of this section to claim rights or contest your 
-	rights to work written entirely by you; rather, the intent is to exercise the 
-	right to control the distribution of derivative or collective works based on 
-	the Program.
-	
-	In addition, mere aggregation of another work not based on the Program with the 
-	Program (or with a work based on the Program) on a volume of a storage or 
-	distribution medium does not bring the other work under the scope of this 
-	License.
-	
-	3. You may copy and distribute the Program (or a work based on it, under 
-	Section 2) in object code or executable form under the terms of Sections 1 
-	and 2 above provided that you also do one of the following:
-	
-	a) Accompany it with the complete corresponding machine-readable source code, 
-	   which must be distributed under the terms of Sections 1 and 2 above on a 
-	   medium customarily used for software interchange; or,
-	b) Accompany it with a written offer, valid for at least three years, to give
-	   any third party, for a charge no more than your cost of physically 
-	   performing source distribution, a complete machine-readable copy of the 
-	   corresponding source code, to be distributed under the terms of Sections 1 
-	   and 2 above on a medium customarily used for software interchange; or,
-	c) Accompany it with the information you received as to the offer to distribute
-	   corresponding source code. (This alternative is allowed only for 
-	   noncommercial distribution and only if you received the program in object 
-	   code or executable form with such an offer, in accord with Subsection b 
-	   above.)
-   
-	The source code for a work means the preferred form of the work for making 
-	modifications to it. For an executable work, complete source code means all the 
-	source code for all modules it contains, plus any associated interface 
-	definition files, plus the scripts used to control compilation and installation 
-	of the executable. However, as a special exception, the source code distributed 
-	need not include anything that is normally distributed (in either source or 
-	binary form) with the major components (compiler, kernel, and so on) of the 
-	operating system on which the executable runs, unless that component itself 
-	accompanies the executable.
-	
-	If distribution of executable or object code is made by offering access to 
-	copy from a designated place, then offering equivalent access to copy the 
-	source code from the same place counts as distribution of the source code, 
-	even though third parties are not compelled to copy the source along with the 
-	object code.
 
-4. 	You may not copy, modify, sublicense, or distribute the Program except as 
+You may charge a fee for the physical act of transferring a copy, and
-	expressly provided under this License. Any attempt otherwise to copy, modify, 
+you may at your option offer warranty protection in exchange for a fee.
-	sublicense or distribute the Program is void, and will automatically 
-	terminate your rights under this License. However, parties who have 
-	received copies, or rights, from you under this License will not have their 
-	licenses terminated so long as such parties remain in full compliance.
 
-5. 	You are not required to accept this License, since you have not signed it. 
+  2. You may modify your copy or copies of the Program or any portion
-	However, nothing else grants you permission to modify or distribute the 
+of it, thus forming a work based on the Program, and copy and
-	Program or its derivative works. These actions are prohibited by law if 
+distribute such modifications or work under the terms of Section 1
-	you do not accept this License. Therefore, by modifying or distributing 
+above, provided that you also meet all of these conditions:
-	the Program (or any work based on the Program), you indicate your 
-	acceptance of this License to do so, and all its terms and conditions 
-	for copying, distributing or modifying the Program or works based on it.
 
-6. 	Each time you redistribute the Program (or any work based on the Program), 
+    a) You must cause the modified files to carry prominent notices
-	the recipient automatically receives a license from the original licensor
+    stating that you changed the files and the date of any change.
-	to copy, distribute or modify the Program subject to these terms and 
-	conditions. You may not impose any further restrictions on the recipients' 
-	exercise of the rights granted herein. You are not responsible for enforcing 
-	compliance by third parties to this License.
 
-7.  If, as a consequence of a court judgment or allegation of patent infringement 
+    b) You must cause any work that you distribute or publish, that in
-	or for any other reason (not limited to patent issues), conditions are
+    whole or in part contains or is derived from the Program or any
-	imposed on you (whether by court order, agreement or otherwise) that 
+    part thereof, to be licensed as a whole at no charge to all third
-	contradict the conditions of this License, they do not excuse you from the
+    parties under the terms of this License.
-	conditions of this License. If you cannot distribute so as to satisfy 
-	simultaneously your obligations under this License and any other pertinent 
-	obligations, then as a consequence you may not distribute the Program at 
-	all. For example, if a patent license would not permit royalty-free 
-	redistribution of the Program by all those who receive copies directly or 
-	indirectly through you, then the only way you could satisfy both it and 
-	this License would be to refrain entirely from distribution of the Program.
 
-	If any portion of this section is held invalid or unenforceable under any 
+    c) If the modified program normally reads commands interactively
-	particular circumstance, the balance of the section is intended to apply 
+    when run, you must cause it, when started running for such
-	and the section as a whole is intended to apply in other circumstances.
+    interactive use in the most ordinary way, to print or display an
+    announcement including an appropriate copyright notice and a
+    notice that there is no warranty (or else, saying that you provide
+    a warranty) and that users may redistribute the program under
+    these conditions, and telling the user how to view a copy of this
+    License.  (Exception: if the Program itself is interactive but
+    does not normally print such an announcement, your work based on
+    the Program is not required to print an announcement.)
 
-	It is not the purpose of this section to induce you to infringe any patents 
+These requirements apply to the modified work as a whole.  If
-	or other property right claims or to contest validity of any such claims; 
+identifiable sections of that work are not derived from the Program,
-	this section has the sole purpose of protecting the integrity of the free 
+and can be reasonably considered independent and separate works in
-	software distribution system, which is implemented by public license 
+themselves, then this License, and its terms, do not apply to those
-	practices. Many people have made generous contributions to the wide range 
+sections when you distribute them as separate works.  But when you
-	of software distributed through that system in reliance on consistent 
+distribute the same sections as part of a whole which is a work based
-	application of that system; it is up to the author/donor to decide if he or 
+on the Program, the distribution of the whole must be on the terms of
-	she is willing to distribute software through any other system and a 
+this License, whose permissions for other licensees extend to the
-	licensee cannot impose that choice.
+entire whole, and thus to each and every part regardless of who wrote it.
-	
-	This section is intended to make thoroughly clear what is believed to be a 
-	consequence of the rest of this License.
-	
-8. 	If the distribution and/or use of the Program is restricted in certain 
-	countries either by patents or by copyrighted interfaces, the original 
-	copyright holder who places the Program under this License may add an 
-	explicit geographical distribution limitation excluding those countries, 
-	so that distribution is permitted only in or among countries not thus 
-	excluded. In such case, this License incorporates the limitation as if 
-	written in the body of this License.
 
-9. 	The Free Software Foundation may publish revised and/or new versions of the 
+Thus, it is not the intent of this section to claim rights or contest
-	General Public License from time to time. Such new versions will be similar 
+your rights to work written entirely by you; rather, the intent is to
-	in spirit to the present version, but may differ in detail to address new 
+exercise the right to control the distribution of derivative or
-	problems or concerns.
+collective works based on the Program.
 
-	Each version is given a distinguishing version number. If the Program 
+In addition, mere aggregation of another work not based on the Program
-	specifies a version number of this License which applies to it and 
+with the Program (or with a work based on the Program) on a volume of
-	"any later version", you have the option of following the terms and 
+a storage or distribution medium does not bring the other work under
-	conditions either of that version or of any later version published 
+the scope of this License.
-	by the Free Software Foundation. If the Program does not specify a version 
-	number of this License, you may choose any version ever published by the 
-	Free Software Foundation.
 
-10. If you wish to incorporate parts of the Program into other free programs 
+  3. You may copy and distribute the Program (or a work based on it,
-	whose distribution conditions are different, write to the author to ask for 
+under Section 2) in object code or executable form under the terms of
-	permission. For software which is copyrighted by the Free Software 
+Sections 1 and 2 above provided that you also do one of the following:
-	Foundation, write to the Free Software Foundation; we sometimes make 
-	exceptions for this. Our decision will be guided by the two goals of 
-	preserving the free status of all derivatives of our free software and of 
-	promoting the sharing and reuse of software generally.
 
-NO WARRANTY
+    a) Accompany it with the complete corresponding machine-readable
+    source code, which must be distributed under the terms of Sections
+    1 and 2 above on a medium customarily used for software interchange; or,
 
-11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR 
+    b) Accompany it with a written offer, valid for at least three
-	THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN 
+    years, to give any third party, for a charge no more than your
-	OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES 
+    cost of physically performing source distribution, a complete
-	PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED 
+    machine-readable copy of the corresponding source code, to be
-	OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 
+    distributed under the terms of Sections 1 and 2 above on a medium
-	MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO 
+    customarily used for software interchange; or,
-	THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM 
-	PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR 
-	CORRECTION.
 
-12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL 
+    c) Accompany it with the information you received as to the offer
-	ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE
+    to distribute corresponding source code.  (This alternative is
-	THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY 
+    allowed only for noncommercial distribution and only if you
-	GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE 
+    received the program in object code or executable form with such
-	USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF 
+    an offer, in accord with Subsection b above.)
-	DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD 
+
-	PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), 
+The source code for a work means the preferred form of the work for
-	EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF 
+making modifications to it.  For an executable work, complete source
-	SUCH DAMAGES.
+code means all the source code for all modules it contains, plus any
+associated interface definition files, plus the scripts used to
+control compilation and installation of the executable.  However, as a
+special exception, the source code distributed need not include
+anything that is normally distributed (in either source or binary
+form) with the major components (compiler, kernel, and so on) of the
+operating system on which the executable runs, unless that component
+itself accompanies the executable.
+
+If distribution of executable or object code is made by offering
+access to copy from a designated place, then offering equivalent
+access to copy the source code from the same place counts as
+distribution of the source code, even though third parties are not
+compelled to copy the source along with the object code.
+
+  4. You may not copy, modify, sublicense, or distribute the Program
+except as expressly provided under this License.  Any attempt
+otherwise to copy, modify, sublicense or distribute the Program is
+void, and will automatically terminate your rights under this License.
+However, parties who have received copies, or rights, from you under
+this License will not have their licenses terminated so long as such
+parties remain in full compliance.
+
+  5. You are not required to accept this License, since you have not
+signed it.  However, nothing else grants you permission to modify or
+distribute the Program or its derivative works.  These actions are
+prohibited by law if you do not accept this License.  Therefore, by
+modifying or distributing the Program (or any work based on the
+Program), you indicate your acceptance of this License to do so, and
+all its terms and conditions for copying, distributing or modifying
+the Program or works based on it.
+
+  6. Each time you redistribute the Program (or any work based on the
+Program), the recipient automatically receives a license from the
+original licensor to copy, distribute or modify the Program subject to
+these terms and conditions.  You may not impose any further
+restrictions on the recipients' exercise of the rights granted herein.
+You are not responsible for enforcing compliance by third parties to
+this License.
+
+  7. If, as a consequence of a court judgment or allegation of patent
+infringement or for any other reason (not limited to patent issues),
+conditions are imposed on you (whether by court order, agreement or
+otherwise) that contradict the conditions of this License, they do not
+excuse you from the conditions of this License.  If you cannot
+distribute so as to satisfy simultaneously your obligations under this
+License and any other pertinent obligations, then as a consequence you
+may not distribute the Program at all.  For example, if a patent
+license would not permit royalty-free redistribution of the Program by
+all those who receive copies directly or indirectly through you, then
+the only way you could satisfy both it and this License would be to
+refrain entirely from distribution of the Program.
+
+If any portion of this section is held invalid or unenforceable under
+any particular circumstance, the balance of the section is intended to
+apply and the section as a whole is intended to apply in other
+circumstances.
+
+It is not the purpose of this section to induce you to infringe any
+patents or other property right claims or to contest validity of any
+such claims; this section has the sole purpose of protecting the
+integrity of the free software distribution system, which is
+implemented by public license practices.  Many people have made
+generous contributions to the wide range of software distributed
+through that system in reliance on consistent application of that
+system; it is up to the author/donor to decide if he or she is willing
+to distribute software through any other system and a licensee cannot
+impose that choice.
+
+This section is intended to make thoroughly clear what is believed to
+be a consequence of the rest of this License.
+
+  8. If the distribution and/or use of the Program is restricted in
+certain countries either by patents or by copyrighted interfaces, the
+original copyright holder who places the Program under this License
+may add an explicit geographical distribution limitation excluding
+those countries, so that distribution is permitted only in or among
+countries not thus excluded.  In such case, this License incorporates
+the limitation as if written in the body of this License.
+
+  9. The Free Software Foundation may publish revised and/or new versions
+of the General Public License from time to time.  Such new versions will
+be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
+
+Each version is given a distinguishing version number.  If the Program
+specifies a version number of this License which applies to it and "any
+later version", you have the option of following the terms and conditions
+either of that version or of any later version published by the Free
+Software Foundation.  If the Program does not specify a version number of
+this License, you may choose any version ever published by the Free Software
+Foundation.
+
+  10. If you wish to incorporate parts of the Program into other free
+programs whose distribution conditions are different, write to the author
+to ask for permission.  For software which is copyrighted by the Free
+Software Foundation, write to the Free Software Foundation; we sometimes
+make exceptions for this.  Our decision will be guided by the two goals
+of preserving the free status of all derivatives of our free software and
+of promoting the sharing and reuse of software generally.
+
+                            NO WARRANTY
+
+  11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
+FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN
+OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
+PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
+OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS
+TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
+PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
+REPAIR OR CORRECTION.
+
+  12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
+REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
+INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
+OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
+TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
+YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
+PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGES.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+convey the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    {description}
+    Copyright (C) {year}  {fullname}
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License along
+    with this program; if not, write to the Free Software Foundation, Inc.,
+    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+Also add information on how to contact you by electronic and paper mail.
+
+If the program is interactive, make it output a short notice like this
+when it starts in an interactive mode:
+
+    Gnomovision version 69, Copyright (C) year name of author
+    Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, the commands you use may
+be called something other than `show w' and `show c'; they could even be
+mouse-clicks or menu items--whatever suits your program.
+
+You should also get your employer (if you work as a programmer) or your
+school, if any, to sign a "copyright disclaimer" for the program, if
+necessary.  Here is a sample; alter the names:
+
+  Yoyodyne, Inc., hereby disclaims all copyright interest in the program
+  `Gnomovision' (which makes passes at compilers) written by James Hacker.
+
+  {signature of Ty Coon}, 1 April 1989
+  Ty Coon, President of Vice
+
+This General Public License does not permit incorporating your program into
+proprietary programs.  If your program is a subroutine library, you may
+consider it more useful to permit linking proprietary applications with the
+library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.
 
-END OF TERMS AND CONDITIONS

README.md

@@ -2,6 +2,17 @@
 
 Core cellular automaton engine for MicroWorld.
 
+## Part of the overall MicroWorld system 
+
+While this code works and is interesting on its own, you also need at least
+[mw-parser](https://github.com/simon-brooke/mw-parser) and 
+[mw-ui](https://github.com/simon-brooke/mw-ui). There will be other 
+modules in due course.
+
+You can see MicroWorld in action [here](http://www.journeyman.cc/microworld/) -
+but please don't be mean to my poor little server. If you want to run big maps
+or complex rule-sets, please run it on your own machines.
+
 ## Usage
 
 Primary entry points are make-world and run-world, both in mw-engine.core. See
@@ -10,6 +21,19 @@ using
 
     lein marg
 
+To build the whole system, place all MicroWorld projects in a common directory,
+and from that directory run *buildall.sh*. Alternatively, in each MicroWorld 
+project directory, run
+
+	lein clean
+	lein compile
+	lein marg
+	lein install
+
+and then from the mw-ui directory, run
+
+	lein ring server
+
 ## License
 
 Copyright © 2014 Simon Brooke

buildall.sh

@@ -6,7 +6,7 @@
 
 # WARNING: The regexps in this are fair awfy bruckle. Edit with care.
 
-# Simon Broooke <simon@jasmine.org.uk>
+# Simon Broooke <simon@journeyman.cc>
 
 # Variable and glag initialisation
 archive=FALSE
@@ -72,10 +72,11 @@ if [ $# -lt 1 ]
 then
 	cat <<-EOF 1>&2
 	Usage:
-    -archive           Create a tar archive of the current state of the source.
+      -archive           Create a tar archive of the current state of the source.
 	  -build             Build all components and commit to master.
 	  -email [ADDRESS]   Your email address, to be recorded in the build signature.
 	  -fullname [NAME]   Your full name, to be recorded in the build signature.
+	  -pull				 Pull from remote git repository
 	  -release [LABEL]   Build all components, branch for release on old label, then
 	                     upversion to new LABEL and commit to master.
 	  -trial             Trial build only, do not commit.
@@ -86,8 +87,8 @@ fi
 while (( "$#" ))
 do
 	case $1 in
-    -a|-archive)
+    	-a|-archive)
-      archive="TRUE";;
+      		archive="TRUE";;
 		-b|-build)
 			# 'build' is the expected normal case.
 			trial="FALSE";
@@ -98,6 +99,9 @@ do
 		-f|-fullname)
 			shift;
 			fullname=$1;;
+	    -p|-pull)
+	      	# pull from remote Git origin
+	      	git pull origin master;;
 		-r|-release)
 			# release is branch a release and upversion to new label
 			shift;
@@ -108,9 +112,6 @@ do
 				echo "Release flagged, but no release tag supplied" 1>&2;
 				exit 1;
 			fi;;
-    -p|-pull)
-      # pull from remote Git origin
-      git pull origin master;;
 		-t|-trial)
 			trial="TRUE";;
 		-w|-webapps)

project.clj

@@ -1,4 +1,4 @@
-(defproject mw-engine "0.1.3"
+(defproject mw-engine "0.1.5-SNAPSHOT"
   :description "Cellular automaton world builder."
   :url "http://www.journeyman.cc/microworld/"
   :manifest {
@@ -11,10 +11,11 @@
   :jvm-opts ["-Xmx4g"]
   :license {:name "GNU General Public License v2"
             :url "http://www.gnu.org/licenses/gpl-2.0.html"}
-  :plugins [[lein-marginalia "0.7.1"]
+  :plugins [[lein-marginalia "0.7.1"]]
-            [lein-gorilla "0.3.2"]]
+  :dependencies [[org.clojure/clojure "1.6.0"]
-  :dependencies [[org.clojure/clojure "1.5.1"]
                  [org.clojure/math.combinatorics "0.0.7"]
                  [org.clojure/tools.trace "0.7.8"]
+                 [org.clojure/tools.namespace "0.2.4"]
+                 [hiccup "1.0.5"]
                  [net.mikera/imagez "0.3.1"]
                  [fivetonine/collage "0.2.0"]])

src/mw_engine/core.clj

@@ -23,12 +23,12 @@
 ;; that every cell's :x and :y properties reflect its place in the matrix.
 ;; See `world.clj`.
 ;;
-;; Each time the world is transformed (see `transform-world`, for each cell, 
+;; Each time the world is transformed (see `transform-world`, for each cell,
 ;; rules are applied in turn until one matches. Once one rule has matched no
 ;; further rules can be applied.
 
 
-(defn apply-rule 
+(defn apply-rule
   "Apply a single `rule` to a `cell`. What this is about is that I want to be able,
    for debugging purposes, to tag a cell with the rule text of the rule which
    fired (and especially so when an exception is thrown. So a rule may be either
@@ -41,7 +41,7 @@
      (seq? rule) (let [[afn src] rule] (apply-rule cell world afn src))))
   ([cell world rule source]
     (let [result (apply rule (list cell world))]
-      (cond 
+      (cond
         (and result source) (merge result {:rule source})
         true result))))
 
@@ -58,11 +58,11 @@
    exception is thrown, cache its message on the cell and set it's state to error"
   [world cell rules]
   (try
-    (merge 
+    (merge
-      (apply-rules world cell rules) 
+      (apply-rules world cell rules)
-      {:generation (+ (or (:generation cell) 0) 1)})
+      {:generation (+ (get-int-or-zero cell :generation) 1)})
-    (catch Exception e 
+    (catch Exception e
-      (merge cell {:error 
+      (merge cell {:error
                    (format "%s at generation %d when in state %s"
                            (.getMessage e)
                            (:generation cell)
@@ -93,28 +93,10 @@
   * `generations` an (integer) number of generations.
 
   Return the final generation of the world."
-  [world init-rules rules generations]  
-  (let [state {:world (transform-world world init-rules) :rules rules}]
-    (:world 
-      (last 
-        (doall 
-          (take generations 
-                (iterate transform-world-state state)))))))
-
-(defn run-world2
-  "Doesn't work yet"
   [world init-rules rules generations]
-  (with-local-vars [r (ref (transform-world world init-rules))]
+  (reduce (fn [world _iteration]
-    (dotimes [g generations]
-      (dosync
-        (ref-set r (transform-world (deref r) rules))))
-    (deref r)))
-
-(defn run-world3
-  [world init-rules rules generations]
-  (reduce (fn [world _iteration] 
             (transform-world world rules))
         (transform-world world init-rules)
         (range generations)))
-        
+
-  
+

src/mw_engine/drainage.clj

@@ -3,7 +3,14 @@
 
 (ns mw-engine.drainage
   (:use mw-engine.utils
-        mw-engine.world))
+        mw-engine.world
+        mw-engine.core)
+  (:require [mw-engine.heightmap :as heightmap]))
+
+(def ^:dynamic *sealevel* 10)
+
+;; forward declaration of flow, to allow for a wee bit of mutual recursion.
+(declare flow)
 
 (defn rain-world
   "Simulate rainfall on this `world`. TODO: Doesn't really work just now - should
@@ -13,30 +20,98 @@
 
 (defn flow-contributors
   "Return a list of the cells in this `world` which are higher than this
-  `cell` and for which this cell is the lowest neighbour"
+  `cell` and for which this cell is the lowest neighbour, or which are at the 
-  [world cell]
+   same altitude and have greater flow"
-  (remove nil?
+  [cell world]
+  (filter #(map? %)
           (map
-           (fn [n]
+            (fn [n]
-             (cond (= cell (get-least-cell (get-neighbours world n) :altitude)) n))
+              (cond 
-           (get-neighbours-with-property-value world (:x cell) (:y cell) 1
+                (= cell (get-least-cell (get-neighbours world n) :altitude)) n
-                                                                  :altitude
+                (and (= (:altitude cell) (:altitude n))
-                                                                  (or (:altitude cell) 0) >))))
+                     (> (or (:flow n) 0) (or (:flow cell) 0))) n))
+            (get-neighbours-with-property-value 
+              world (:x cell) (:y cell) 1 :altitude
+              (or (:altitude cell) 0) >=))))
 
-(defn flow
+(defn is-hollow
+  "Detects point hollows - that is, individual cells all of whose neighbours 
+   are higher. Return true if this `cell` has an altitude lower than any of 
+   its neighbours in this `world`" 
+  [world cell]
+  ;; quicker to count the elements of the list and compare equality of numbers
+  ;; than recursive equality check on members, I think. But worth benchmarking.
+  (let [neighbours (get-neighbours world cell)
+        altitude (get-int-or-zero cell :altitude)]
+    (= (count neighbours)
+       (count (get-neighbours-with-property-value 
+                world (:x cell) (:y cell) 1 :altitude altitude >)))))
+
+(defn flood-hollow
+  "Raise the altitude of a copy of this `cell` of this `world` to the altitude  
+   of the lowest of its `neighbours`."
+  ([world cell neighbours]
+    (let [lowest (get-least-cell neighbours :altitude)]
+      (merge cell {:state :water :altitude (:altitude lowest)})))
+  ([world cell]
+    (flood-hollow world cell (get-neighbours world cell))))
+
+(defn flood-hollows 
+  "Flood all local hollows in this `world`. At this stage only floods single
+   cell hollows."
+  [world]
+  (map-world world 
+             #(if (is-hollow %1 %2) (flood-hollow %1 %2) %2)))
+
+(def max-altitude 255)
+
+(defn flow-nr
+  "Experimental non recursive flow algorithm, needs to be run on a world as 
+   many times as there are distinct altitude values. This algorithm works only
+   if applied sequentially from the highest altitude to the lowest, see
+   `flow-world-nr`."
+  [cell world]
+  (if (= (- max-altitude (get-int-or-zero cell :generation))
+         (get-int-or-zero cell :altitude))
+    (merge cell 
+           {:flow (reduce + 
+                          (map 
+                            #(+ (get-int-or-zero % :rainfall)
+                                (get-int-or-zero % :flow))
+                            (flow-contributors cell world)))})))
+
+(def flow
   "Compute the total flow upstream of this `cell` in this `world`, and return a cell identical
-   to this one but having a value of its flow property set from that computation.
+  to this one but having a value of its flow property set from that computation. The function is
+  memoised because the consequence of mapping a recursive function across an array is that many
+  cells will be revisited - potentially many times.
 
-   Flow comes from a higher cell to a lower only if the lower is the lowest neighbour of the higher."
+  Flow comes from a higher cell to a lower only if the lower is the lowest neighbour of the higher."
-   [world cell]
+  (memoize
+   (fn [cell world]
+     (cond
+      (not (nil? (:flow cell))) cell
+      (<= (or (:altitude cell) 0) *sealevel*) cell
+      true
       (merge cell
-           {:flow (+ (:rainfall cell)
+             {:flow (+ (:rainfall cell)
-               (apply +
+                       (apply +
-                 (map (fn [neighbour] (:flow (flow world neighbour)))
+                              (map (fn [neighbour] (:flow (flow neighbour world)))
-                      (flow-contributors world cell))))}))
+                                   (flow-contributors cell world))))})))))
+
+(defn flow-world-nr
+  "Experimental non-recursive flow-world algorithm"
+  [world]
+  (run-world world nil (list flow-nr) max-altitude))
 
 (defn flow-world
   "Return a world like this `world`, but with cells tagged with the amount of
    water flowing through them."
   [world]
   (map-world (rain-world world) flow))
+
+(defn run-drainage
+  [hmap]
+  "Create a world from the heightmap `hmap`, rain on it, and then compute river 
+   flows."
+  (flow-world (rain-world (flood-hollows (heightmap/apply-heightmap hmap)))))

src/mw_engine/heightmap.clj

@@ -6,14 +6,13 @@
 (ns mw-engine.heightmap
   (:import [java.awt.image BufferedImage])
   (:use mw-engine.utils
-        mw-engine.world
+        mw-engine.world)
-        mw-engine.drainage)
   (:require [fivetonine.collage.util :as collage :only [load-image]]
             [mikera.image.core :as imagez :only [filter-image get-pixels]]
             [mikera.image.filters :as filters]))
 
 
-(defn- tag-property
+(defn tag-property
   "Set the value of this `property` of this cell from the corresponding pixel of this `heightmap`.
    If the heightmap you supply is smaller than the world, this will break.
 
@@ -36,7 +35,7 @@
                         (get-int cell :x)
                         (get-int cell :y)) 256))))})))
 
-(defn- tag-gradient
+(defn tag-gradient
   "Set the `gradient` property of this `cell` of this `world` to the difference in
    altitude between its highest and lowest neghbours."
   [world cell]
@@ -54,7 +53,7 @@
   [world]
   (map-world world tag-gradient))
 
-(defn- tag-altitude
+(defn tag-altitude
   "Set the altitude of this cell from the corresponding pixel of this heightmap.
    If the heightmap you supply is smaller than the world, this will break.
 

src/mw_engine/utils.clj

@@ -1,8 +1,9 @@
-;; Utility functions needed by MicroWorld and, specifically, in the interpretation of MicroWorld rule.
+;; Utility functions needed by MicroWorld and, specifically, in the
+;; interpretation of MicroWorld rule.
 
 (ns mw-engine.utils
-  (:require 
+  (:require
-    [clojure.core.reducers :as r]
+;;    [clojure.core.reducers :as r]
     [clojure.math.combinatorics :as combo]))
 
 (defn abs
@@ -13,12 +14,28 @@
 
    * `n` a number, on the set of real numbers."
   [n]
-  (cond (neg? n) (- 0 n) true n))
+  (if (neg? n) (- 0 n) n))
 
 (defn member?
   "True if elt is a member of col."
   [elt col] (some #(= elt %) col))
 
+(defn get-int-or-zero
+  "Return the value of this `property` from this `map` if it is a integer;
+   otherwise return zero."
+  [map property]
+  (let [value (map property)]
+    (if (integer? value) value 0)))
+
+(defn init-generation
+  "Return a cell like this `cell`, but having a value for :generation, zero if
+   the cell passed had no integer value for generation, otherwise the value
+   taken from the cell passed. The `world` argument is present only for
+   consistency with the rule engine and is ignored."
+  [world cell]
+  (merge cell {:generation (get-int-or-zero cell :generation)}))
+
+
 (defn in-bounds
   "True if x, y are in bounds for this world (i.e., there is a cell at x, y)
    else false.
@@ -29,17 +46,47 @@
   [world x y]
   (and (>= x 0)(>= y 0)(< y (count world))(< x (count (first world)))))
 
+(defn map-world-n-n
+  "Wholly non-parallel map world implementation"
+  ([world function]
+    (map-world-n-n world function nil))
+  ([world function additional-args]
+    (into []
+           (map (fn [row]
+                    (into [] (map
+                             #(apply function
+                                     (cons world (cons % additional-args)))
+                             row)))
+                  world))))
+
+(defn map-world-p-p
+  "Wholly parallel map world implementation"
+  ([world function]
+    (map-world-p-p world function nil))
+  ([world function additional-args]
+    (into []
+           (pmap (fn [row]
+                    (into [] (pmap
+                             #(apply function
+                                     (cons world (cons % additional-args)))
+                             row)))
+                  world))))
+
+
 (defn map-world
   "Apply this `function` to each cell in this `world` to produce a new world.
    the arguments to the function will be the world, the cell, and any
-   `additional-args` supplied"
+   `additional-args` supplied. Note that we parallel map over rows but
+   just map over cells within a row. That's because it isn't worth starting
+   a new thread for each cell, but there may be efficiency gains in
+   running rows in parallel."
   ([world function]
     (map-world world function nil))
   ([world function additional-args]
-    (into [] ;; vectors are more efficient for scanning, which we do a lot.
+    (into []
-           (r/map (fn [row]
+           (pmap (fn [row]
-                    (into [] (r/map 
+                    (into [] (map
-                             #(apply function 
+                             #(apply function
                                      (cons world (cons % additional-args)))
                              row)))
                   world))))
@@ -76,35 +123,51 @@
   [cell species]
   (get-int cell species))
 
+(def memo-get-neighbours
+  "Memoised get neighbours is more efficient when running deeply recursive
+   algorithms on the same world. But it's less efficient when running the
+   engine in its normal iterative style, because then we will rarely call
+   get naighbours on the same cell of the same world twice."
+  (memoize
+   (fn [world x y depth]
+     (remove nil?
+             (map #(get-cell world (first %) (first (rest %)))
+                  (remove #(= % (list x y))
+                          (combo/cartesian-product
+                            (range (- x depth) (+ x depth 1))
+                            (range (- y depth) (+ y depth 1)))))))))
 
 (defn get-neighbours
-    "Get the neighbours to distance depth of the cell at x, y in this world.
+    "Get the neighbours to distance depth of a cell in this world.
+
+    Several overloads:
+    * `world` a world, as described in world.clj;
+    * `cell` a cell within that world
+    Gets immediate neighbours of the specified cell.
+
+    * `world` a world, as described in world.clj;
+    * `cell` a cell within that world
+    * `depth` an integer representing the depth to search from the
+      `cell`
+    Gets neighbours within the specified distance of the cell.
 
     * `world` a world, as described in world.clj;
     * `x` an integer representing an x coordinate in that world;
     * `y` an integer representing an y coordinate in that world;
     * `depth` an integer representing the distance from [x,y] that
-      should be searched."
+      should be searched
+    Gets the neighbours within the specified distance of the cell at
+    coordinates [x,y] in this world."
     ([world x y depth]
       (remove nil?
-              (map #(get-cell world (first %) (first (rest %)))
+             (map #(get-cell world (first %) (first (rest %)))
-                   (remove #(= % (list x y))
+                  (remove #(= % (list x y))
-                           (combo/cartesian-product
+                          (combo/cartesian-product
-                             (range (- x depth) (+ x depth 1))
+                            (range (- x depth) (+ x depth 1))
-                             (range (- y depth) (+ y depth 1)))))))
+                            (range (- y depth) (+ y depth 1)))))))
     ([world cell depth]
-      "Get the neighbours to distance depth of this cell in this world.
+      (memo-get-neighbours world (:x cell) (:y cell) depth))
-
-      * `world` a world, as described in world.clj;
-      * `cell` a cell within that world;
-      * `depth` an integer representing the distance from [x,y] that
-        should be searched."
-      (get-neighbours world (:x cell) (:y cell) depth))
     ([world cell]
-      "Get the immediate neighbours of this cell in this world
-
-      * `world` a world, as described in world.clj;
-      * `cell` a cell within that world."
       (get-neighbours world cell 1)))
 
 (defn get-neighbours-with-property-value
@@ -114,10 +177,10 @@
     * `world` a world, as described in `world.clj`;
     * `cell` a cell within that world;
     * `depth` an integer representing the distance from [x,y] that
-      should be searched;
+      should be searched (optional);
     * `property` a keyword representing a property of the neighbours;
     * `value` a value of that property (or, possibly, the name of another);
-    * `op` a comparator function to use in place of `=`.
+    * `op` a comparator function to use in place of `=` (optional).
 
    It gets messy."
   ([world x y depth property value op]
@@ -195,4 +258,16 @@
                  row)))
         world))))
 
-
+(defn merge-cell
+  "Return a world like this `world`, but merge the values from this `cell` with
+   those from the cell in the world with the same co-ordinates"
+  [world cell]
+  (if (in-bounds world (:x cell) (:y cell))
+    (map-world world
+               #(if
+                  (and
+                    (= (:x cell)(:x %2))
+                    (= (:y cell)(:y %2)))
+                  (merge %2 cell)
+                  %2))
+    world))

test/mw_engine/drainage_test.clj

@@ -0,0 +1,48 @@
+(ns mw-engine.drainage-test
+  (:require [clojure.test :refer :all]
+            [mw-engine.world :as world]
+            [mw-engine.utils :as utils]
+            [mw-engine.drainage :refer :all]))
+
+(deftest is-hollow-test
+  (testing "detection of hollows"
+           (let [world (utils/set-property
+                   (utils/map-world 
+                     (world/make-world 3 3)
+                     #(merge %2 {:altitude 100}))
+                   1 1 :altitude 90)]
+             (is (is-hollow world (utils/get-cell world 1 1))
+                 "Cell at 1, 1 should be a hollow"))))
+
+(deftest flood-hollow-test
+  (testing "Flooding of a single specified cell"
+             (let [world (utils/set-property
+                   (utils/map-world 
+                     (world/make-world 3 3)
+                     #(merge %2 {:altitude 100}))
+                   1 1 :altitude 90)
+                   cell (flood-hollow world (utils/get-cell world 1 1))]
+               (is (= (:state cell) :water)
+                   "State should be water")
+               (is (= (:altitude cell) 100)
+                   "Altitude should be 100"))))
+               
+(deftest flood-hollows-test
+  (testing "Flooding of hollows"
+           (let [world (utils/set-property
+                   (utils/map-world 
+                     (world/make-world 3 3)
+                     #(merge %2 {:altitude 100}))
+                   1 1 :altitude 90)
+                 w2 (flood-hollows world)]
+             (is (= (:state (utils/get-cell world 1 1)) :new)
+                 "State of cell in original world should still be :new")
+             (is (= (:state (utils/get-cell w2 1 1)) :water)
+                 "State of cell in processed world should still be :water")
+             (is (= (:altitude (utils/get-cell w2 1 1)) 100)
+                 "Altitude of cell in processed world should still be 100"))))
+             
+                                  
+
+  
+  

test/mw_engine/utils_test.clj

@@ -164,6 +164,18 @@
                  "All cells should have property 'test' set to true")
              (is (empty? (remove #(= % 8) (map #(:number %) (flatten w3c))))
                  "All cells should have property 'number' set to 8"))))
-             
+
-  
+(deftest merge-cell-test
-            
+  (testing "merge-cell utility function"
+           (let [w1a (make-world 3 3)
+                 w2b (merge-cell w1a {:x 5 :y 5 :out-of-bounds true})
+                 w3c (merge-cell w1a {:x 2 :y 2 :test true})]
+             (is (= w1a w2b) "Out of bound cell makes no difference")
+             (is (empty? (filter #(:out-of-bounds %) (flatten w2b)))
+                 "No cell has :out-of-bounds set")
+             (is (= 1 (count (filter #(:test %) (flatten w3c))))
+                 "Exactly one cell has :test set")
+             (is (:test (get-cell w3c 2 2))
+                 "The cell with :test set is at 2, 2"))))
+
+