commit d730f13072228eb0c4ba68aa15b0409db99ded73
Author: Richard Ipsum <richardipsum@fastmail.co.uk>
Date:   Sat, 19 Jan 2019 20:54:54 +0000
Initial commit
Diffstat:
| A | COPYING | | | 674 | +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ | 
| A | Makefile | | | 36 | ++++++++++++++++++++++++++++++++++++ | 
| A | README | | | 51 | +++++++++++++++++++++++++++++++++++++++++++++++++++ | 
| A | find_lua | | | 9 | +++++++++ | 
| A | tyarn.c | | | 659 | +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ | 
| A | tyarn.in | | | 434 | +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ | 
6 files changed, 1863 insertions(+), 0 deletions(-)
diff --git a/COPYING b/COPYING
@@ -0,0 +1,674 @@
+                    GNU GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <http://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+                            Preamble
+
+  The GNU General Public License is a free, copyleft license for
+software and other kinds of works.
+
+  The licenses for most software and other practical works are designed
+to take away your freedom to share and change the works.  By contrast,
+the GNU General Public License is intended to guarantee your freedom to
+share and change all versions of a program--to make sure it remains free
+software for all its users.  We, the Free Software Foundation, use the
+GNU General Public License for most of our software; it applies also to
+any other work released this way by its authors.  You can apply it to
+your programs, too.
+
+  When we speak of free software, we are referring to freedom, not
+price.  Our General Public Licenses are designed to make sure that you
+have the freedom to distribute copies of free software (and charge for
+them if you wish), that you receive source code or can get it if you
+want it, that you can change 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 prevent others from denying you
+these rights or asking you to surrender the rights.  Therefore, you have
+certain responsibilities if you distribute copies of the software, or if
+you modify it: responsibilities to respect the freedom of others.
+
+  For example, if you distribute copies of such a program, whether
+gratis or for a fee, you must pass on to the recipients the same
+freedoms that you received.  You must make sure that they, too, receive
+or can get the source code.  And you must show them these terms so they
+know their rights.
+
+  Developers that use the GNU GPL protect your rights with two steps:
+(1) assert copyright on the software, and (2) offer you this License
+giving you legal permission to copy, distribute and/or modify it.
+
+  For the developers' and authors' protection, the GPL clearly explains
+that there is no warranty for this free software.  For both users' and
+authors' sake, the GPL requires that modified versions be marked as
+changed, so that their problems will not be attributed erroneously to
+authors of previous versions.
+
+  Some devices are designed to deny users access to install or run
+modified versions of the software inside them, although the manufacturer
+can do so.  This is fundamentally incompatible with the aim of
+protecting users' freedom to change the software.  The systematic
+pattern of such abuse occurs in the area of products for individuals to
+use, which is precisely where it is most unacceptable.  Therefore, we
+have designed this version of the GPL to prohibit the practice for those
+products.  If such problems arise substantially in other domains, we
+stand ready to extend this provision to those domains in future versions
+of the GPL, as needed to protect the freedom of users.
+
+  Finally, every program is threatened constantly by software patents.
+States should not allow patents to restrict development and use of
+software on general-purpose computers, but in those that do, we wish to
+avoid the special danger that patents applied to a free program could
+make it effectively proprietary.  To prevent this, the GPL assures that
+patents cannot be used to render the program non-free.
+
+  The precise terms and conditions for copying, distribution and
+modification follow.
+
+                       TERMS AND CONDITIONS
+
+  0. Definitions.
+
+  "This License" refers to version 3 of the GNU General Public License.
+
+  "Copyright" also means copyright-like laws that apply to other kinds of
+works, such as semiconductor masks.
+
+  "The Program" refers to any copyrightable work licensed under this
+License.  Each licensee is addressed as "you".  "Licensees" and
+"recipients" may be individuals or organizations.
+
+  To "modify" a work means to copy from or adapt all or part of the work
+in a fashion requiring copyright permission, other than the making of an
+exact copy.  The resulting work is called a "modified version" of the
+earlier work or a work "based on" the earlier work.
+
+  A "covered work" means either the unmodified Program or a work based
+on the Program.
+
+  To "propagate" a work means to do anything with it that, without
+permission, would make you directly or secondarily liable for
+infringement under applicable copyright law, except executing it on a
+computer or modifying a private copy.  Propagation includes copying,
+distribution (with or without modification), making available to the
+public, and in some countries other activities as well.
+
+  To "convey" a work means any kind of propagation that enables other
+parties to make or receive copies.  Mere interaction with a user through
+a computer network, with no transfer of a copy, is not conveying.
+
+  An interactive user interface displays "Appropriate Legal Notices"
+to the extent that it includes a convenient and prominently visible
+feature that (1) displays an appropriate copyright notice, and (2)
+tells the user that there is no warranty for the work (except to the
+extent that warranties are provided), that licensees may convey the
+work under this License, and how to view a copy of this License.  If
+the interface presents a list of user commands or options, such as a
+menu, a prominent item in the list meets this criterion.
+
+  1. Source Code.
+
+  The "source code" for a work means the preferred form of the work
+for making modifications to it.  "Object code" means any non-source
+form of a work.
+
+  A "Standard Interface" means an interface that either is an official
+standard defined by a recognized standards body, or, in the case of
+interfaces specified for a particular programming language, one that
+is widely used among developers working in that language.
+
+  The "System Libraries" of an executable work include anything, other
+than the work as a whole, that (a) is included in the normal form of
+packaging a Major Component, but which is not part of that Major
+Component, and (b) serves only to enable use of the work with that
+Major Component, or to implement a Standard Interface for which an
+implementation is available to the public in source code form.  A
+"Major Component", in this context, means a major essential component
+(kernel, window system, and so on) of the specific operating system
+(if any) on which the executable work runs, or a compiler used to
+produce the work, or an object code interpreter used to run it.
+
+  The "Corresponding Source" for a work in object code form means all
+the source code needed to generate, install, and (for an executable
+work) run the object code and to modify the work, including scripts to
+control those activities.  However, it does not include the work's
+System Libraries, or general-purpose tools or generally available free
+programs which are used unmodified in performing those activities but
+which are not part of the work.  For example, Corresponding Source
+includes interface definition files associated with source files for
+the work, and the source code for shared libraries and dynamically
+linked subprograms that the work is specifically designed to require,
+such as by intimate data communication or control flow between those
+subprograms and other parts of the work.
+
+  The Corresponding Source need not include anything that users
+can regenerate automatically from other parts of the Corresponding
+Source.
+
+  The Corresponding Source for a work in source code form is that
+same work.
+
+  2. Basic Permissions.
+
+  All rights granted under this License are granted for the term of
+copyright on the Program, and are irrevocable provided the stated
+conditions are met.  This License explicitly affirms your unlimited
+permission to run the unmodified Program.  The output from running a
+covered work is covered by this License only if the output, given its
+content, constitutes a covered work.  This License acknowledges your
+rights of fair use or other equivalent, as provided by copyright law.
+
+  You may make, run and propagate covered works that you do not
+convey, without conditions so long as your license otherwise remains
+in force.  You may convey covered works to others for the sole purpose
+of having them make modifications exclusively for you, or provide you
+with facilities for running those works, provided that you comply with
+the terms of this License in conveying all material for which you do
+not control copyright.  Those thus making or running the covered works
+for you must do so exclusively on your behalf, under your direction
+and control, on terms that prohibit them from making any copies of
+your copyrighted material outside their relationship with you.
+
+  Conveying under any other circumstances is permitted solely under
+the conditions stated below.  Sublicensing is not allowed; section 10
+makes it unnecessary.
+
+  3. Protecting Users' Legal Rights From Anti-Circumvention Law.
+
+  No covered work shall be deemed part of an effective technological
+measure under any applicable law fulfilling obligations under article
+11 of the WIPO copyright treaty adopted on 20 December 1996, or
+similar laws prohibiting or restricting circumvention of such
+measures.
+
+  When you convey a covered work, you waive any legal power to forbid
+circumvention of technological measures to the extent such circumvention
+is effected by exercising rights under this License with respect to
+the covered work, and you disclaim any intention to limit operation or
+modification of the work as a means of enforcing, against the work's
+users, your or third parties' legal rights to forbid circumvention of
+technological measures.
+
+  4. Conveying Verbatim Copies.
+
+  You may convey verbatim copies of the Program's source code as you
+receive it, in any medium, provided that you conspicuously and
+appropriately publish on each copy an appropriate copyright notice;
+keep intact all notices stating that this License and any
+non-permissive terms added in accord with section 7 apply to the code;
+keep intact all notices of the absence of any warranty; and give all
+recipients a copy of this License along with the Program.
+
+  You may charge any price or no price for each copy that you convey,
+and you may offer support or warranty protection for a fee.
+
+  5. Conveying Modified Source Versions.
+
+  You may convey a work based on the Program, or the modifications to
+produce it from the Program, in the form of source code under the
+terms of section 4, provided that you also meet all of these conditions:
+
+    a) The work must carry prominent notices stating that you modified
+    it, and giving a relevant date.
+
+    b) The work must carry prominent notices stating that it is
+    released under this License and any conditions added under section
+    7.  This requirement modifies the requirement in section 4 to
+    "keep intact all notices".
+
+    c) You must license the entire work, as a whole, under this
+    License to anyone who comes into possession of a copy.  This
+    License will therefore apply, along with any applicable section 7
+    additional terms, to the whole of the work, and all its parts,
+    regardless of how they are packaged.  This License gives no
+    permission to license the work in any other way, but it does not
+    invalidate such permission if you have separately received it.
+
+    d) If the work has interactive user interfaces, each must display
+    Appropriate Legal Notices; however, if the Program has interactive
+    interfaces that do not display Appropriate Legal Notices, your
+    work need not make them do so.
+
+  A compilation of a covered work with other separate and independent
+works, which are not by their nature extensions of the covered work,
+and which are not combined with it such as to form a larger program,
+in or on a volume of a storage or distribution medium, is called an
+"aggregate" if the compilation and its resulting copyright are not
+used to limit the access or legal rights of the compilation's users
+beyond what the individual works permit.  Inclusion of a covered work
+in an aggregate does not cause this License to apply to the other
+parts of the aggregate.
+
+  6. Conveying Non-Source Forms.
+
+  You may convey a covered work in object code form under the terms
+of sections 4 and 5, provided that you also convey the
+machine-readable Corresponding Source under the terms of this License,
+in one of these ways:
+
+    a) Convey the object code in, or embodied in, a physical product
+    (including a physical distribution medium), accompanied by the
+    Corresponding Source fixed on a durable physical medium
+    customarily used for software interchange.
+
+    b) Convey the object code in, or embodied in, a physical product
+    (including a physical distribution medium), accompanied by a
+    written offer, valid for at least three years and valid for as
+    long as you offer spare parts or customer support for that product
+    model, to give anyone who possesses the object code either (1) a
+    copy of the Corresponding Source for all the software in the
+    product that is covered by this License, on a durable physical
+    medium customarily used for software interchange, for a price no
+    more than your reasonable cost of physically performing this
+    conveying of source, or (2) access to copy the
+    Corresponding Source from a network server at no charge.
+
+    c) Convey individual copies of the object code with a copy of the
+    written offer to provide the Corresponding Source.  This
+    alternative is allowed only occasionally and noncommercially, and
+    only if you received the object code with such an offer, in accord
+    with subsection 6b.
+
+    d) Convey the object code by offering access from a designated
+    place (gratis or for a charge), and offer equivalent access to the
+    Corresponding Source in the same way through the same place at no
+    further charge.  You need not require recipients to copy the
+    Corresponding Source along with the object code.  If the place to
+    copy the object code is a network server, the Corresponding Source
+    may be on a different server (operated by you or a third party)
+    that supports equivalent copying facilities, provided you maintain
+    clear directions next to the object code saying where to find the
+    Corresponding Source.  Regardless of what server hosts the
+    Corresponding Source, you remain obligated to ensure that it is
+    available for as long as needed to satisfy these requirements.
+
+    e) Convey the object code using peer-to-peer transmission, provided
+    you inform other peers where the object code and Corresponding
+    Source of the work are being offered to the general public at no
+    charge under subsection 6d.
+
+  A separable portion of the object code, whose source code is excluded
+from the Corresponding Source as a System Library, need not be
+included in conveying the object code work.
+
+  A "User Product" is either (1) a "consumer product", which means any
+tangible personal property which is normally used for personal, family,
+or household purposes, or (2) anything designed or sold for incorporation
+into a dwelling.  In determining whether a product is a consumer product,
+doubtful cases shall be resolved in favor of coverage.  For a particular
+product received by a particular user, "normally used" refers to a
+typical or common use of that class of product, regardless of the status
+of the particular user or of the way in which the particular user
+actually uses, or expects or is expected to use, the product.  A product
+is a consumer product regardless of whether the product has substantial
+commercial, industrial or non-consumer uses, unless such uses represent
+the only significant mode of use of the product.
+
+  "Installation Information" for a User Product means any methods,
+procedures, authorization keys, or other information required to install
+and execute modified versions of a covered work in that User Product from
+a modified version of its Corresponding Source.  The information must
+suffice to ensure that the continued functioning of the modified object
+code is in no case prevented or interfered with solely because
+modification has been made.
+
+  If you convey an object code work under this section in, or with, or
+specifically for use in, a User Product, and the conveying occurs as
+part of a transaction in which the right of possession and use of the
+User Product is transferred to the recipient in perpetuity or for a
+fixed term (regardless of how the transaction is characterized), the
+Corresponding Source conveyed under this section must be accompanied
+by the Installation Information.  But this requirement does not apply
+if neither you nor any third party retains the ability to install
+modified object code on the User Product (for example, the work has
+been installed in ROM).
+
+  The requirement to provide Installation Information does not include a
+requirement to continue to provide support service, warranty, or updates
+for a work that has been modified or installed by the recipient, or for
+the User Product in which it has been modified or installed.  Access to a
+network may be denied when the modification itself materially and
+adversely affects the operation of the network or violates the rules and
+protocols for communication across the network.
+
+  Corresponding Source conveyed, and Installation Information provided,
+in accord with this section must be in a format that is publicly
+documented (and with an implementation available to the public in
+source code form), and must require no special password or key for
+unpacking, reading or copying.
+
+  7. Additional Terms.
+
+  "Additional permissions" are terms that supplement the terms of this
+License by making exceptions from one or more of its conditions.
+Additional permissions that are applicable to the entire Program shall
+be treated as though they were included in this License, to the extent
+that they are valid under applicable law.  If additional permissions
+apply only to part of the Program, that part may be used separately
+under those permissions, but the entire Program remains governed by
+this License without regard to the additional permissions.
+
+  When you convey a copy of a covered work, you may at your option
+remove any additional permissions from that copy, or from any part of
+it.  (Additional permissions may be written to require their own
+removal in certain cases when you modify the work.)  You may place
+additional permissions on material, added by you to a covered work,
+for which you have or can give appropriate copyright permission.
+
+  Notwithstanding any other provision of this License, for material you
+add to a covered work, you may (if authorized by the copyright holders of
+that material) supplement the terms of this License with terms:
+
+    a) Disclaiming warranty or limiting liability differently from the
+    terms of sections 15 and 16 of this License; or
+
+    b) Requiring preservation of specified reasonable legal notices or
+    author attributions in that material or in the Appropriate Legal
+    Notices displayed by works containing it; or
+
+    c) Prohibiting misrepresentation of the origin of that material, or
+    requiring that modified versions of such material be marked in
+    reasonable ways as different from the original version; or
+
+    d) Limiting the use for publicity purposes of names of licensors or
+    authors of the material; or
+
+    e) Declining to grant rights under trademark law for use of some
+    trade names, trademarks, or service marks; or
+
+    f) Requiring indemnification of licensors and authors of that
+    material by anyone who conveys the material (or modified versions of
+    it) with contractual assumptions of liability to the recipient, for
+    any liability that these contractual assumptions directly impose on
+    those licensors and authors.
+
+  All other non-permissive additional terms are considered "further
+restrictions" within the meaning of section 10.  If the Program as you
+received it, or any part of it, contains a notice stating that it is
+governed by this License along with a term that is a further
+restriction, you may remove that term.  If a license document contains
+a further restriction but permits relicensing or conveying under this
+License, you may add to a covered work material governed by the terms
+of that license document, provided that the further restriction does
+not survive such relicensing or conveying.
+
+  If you add terms to a covered work in accord with this section, you
+must place, in the relevant source files, a statement of the
+additional terms that apply to those files, or a notice indicating
+where to find the applicable terms.
+
+  Additional terms, permissive or non-permissive, may be stated in the
+form of a separately written license, or stated as exceptions;
+the above requirements apply either way.
+
+  8. Termination.
+
+  You may not propagate or modify a covered work except as expressly
+provided under this License.  Any attempt otherwise to propagate or
+modify it is void, and will automatically terminate your rights under
+this License (including any patent licenses granted under the third
+paragraph of section 11).
+
+  However, if you cease all violation of this License, then your
+license from a particular copyright holder is reinstated (a)
+provisionally, unless and until the copyright holder explicitly and
+finally terminates your license, and (b) permanently, if the copyright
+holder fails to notify you of the violation by some reasonable means
+prior to 60 days after the cessation.
+
+  Moreover, your license from a particular copyright holder is
+reinstated permanently if the copyright holder notifies you of the
+violation by some reasonable means, this is the first time you have
+received notice of violation of this License (for any work) from that
+copyright holder, and you cure the violation prior to 30 days after
+your receipt of the notice.
+
+  Termination of your rights under this section does not terminate the
+licenses of parties who have received copies or rights from you under
+this License.  If your rights have been terminated and not permanently
+reinstated, you do not qualify to receive new licenses for the same
+material under section 10.
+
+  9. Acceptance Not Required for Having Copies.
+
+  You are not required to accept this License in order to receive or
+run a copy of the Program.  Ancillary propagation of a covered work
+occurring solely as a consequence of using peer-to-peer transmission
+to receive a copy likewise does not require acceptance.  However,
+nothing other than this License grants you permission to propagate or
+modify any covered work.  These actions infringe copyright if you do
+not accept this License.  Therefore, by modifying or propagating a
+covered work, you indicate your acceptance of this License to do so.
+
+  10. Automatic Licensing of Downstream Recipients.
+
+  Each time you convey a covered work, the recipient automatically
+receives a license from the original licensors, to run, modify and
+propagate that work, subject to this License.  You are not responsible
+for enforcing compliance by third parties with this License.
+
+  An "entity transaction" is a transaction transferring control of an
+organization, or substantially all assets of one, or subdividing an
+organization, or merging organizations.  If propagation of a covered
+work results from an entity transaction, each party to that
+transaction who receives a copy of the work also receives whatever
+licenses to the work the party's predecessor in interest had or could
+give under the previous paragraph, plus a right to possession of the
+Corresponding Source of the work from the predecessor in interest, if
+the predecessor has it or can get it with reasonable efforts.
+
+  You may not impose any further restrictions on the exercise of the
+rights granted or affirmed under this License.  For example, you may
+not impose a license fee, royalty, or other charge for exercise of
+rights granted under this License, and you may not initiate litigation
+(including a cross-claim or counterclaim in a lawsuit) alleging that
+any patent claim is infringed by making, using, selling, offering for
+sale, or importing the Program or any portion of it.
+
+  11. Patents.
+
+  A "contributor" is a copyright holder who authorizes use under this
+License of the Program or a work on which the Program is based.  The
+work thus licensed is called the contributor's "contributor version".
+
+  A contributor's "essential patent claims" are all patent claims
+owned or controlled by the contributor, whether already acquired or
+hereafter acquired, that would be infringed by some manner, permitted
+by this License, of making, using, or selling its contributor version,
+but do not include claims that would be infringed only as a
+consequence of further modification of the contributor version.  For
+purposes of this definition, "control" includes the right to grant
+patent sublicenses in a manner consistent with the requirements of
+this License.
+
+  Each contributor grants you a non-exclusive, worldwide, royalty-free
+patent license under the contributor's essential patent claims, to
+make, use, sell, offer for sale, import and otherwise run, modify and
+propagate the contents of its contributor version.
+
+  In the following three paragraphs, a "patent license" is any express
+agreement or commitment, however denominated, not to enforce a patent
+(such as an express permission to practice a patent or covenant not to
+sue for patent infringement).  To "grant" such a patent license to a
+party means to make such an agreement or commitment not to enforce a
+patent against the party.
+
+  If you convey a covered work, knowingly relying on a patent license,
+and the Corresponding Source of the work is not available for anyone
+to copy, free of charge and under the terms of this License, through a
+publicly available network server or other readily accessible means,
+then you must either (1) cause the Corresponding Source to be so
+available, or (2) arrange to deprive yourself of the benefit of the
+patent license for this particular work, or (3) arrange, in a manner
+consistent with the requirements of this License, to extend the patent
+license to downstream recipients.  "Knowingly relying" means you have
+actual knowledge that, but for the patent license, your conveying the
+covered work in a country, or your recipient's use of the covered work
+in a country, would infringe one or more identifiable patents in that
+country that you have reason to believe are valid.
+
+  If, pursuant to or in connection with a single transaction or
+arrangement, you convey, or propagate by procuring conveyance of, a
+covered work, and grant a patent license to some of the parties
+receiving the covered work authorizing them to use, propagate, modify
+or convey a specific copy of the covered work, then the patent license
+you grant is automatically extended to all recipients of the covered
+work and works based on it.
+
+  A patent license is "discriminatory" if it does not include within
+the scope of its coverage, prohibits the exercise of, or is
+conditioned on the non-exercise of one or more of the rights that are
+specifically granted under this License.  You may not convey a covered
+work if you are a party to an arrangement with a third party that is
+in the business of distributing software, under which you make payment
+to the third party based on the extent of your activity of conveying
+the work, and under which the third party grants, to any of the
+parties who would receive the covered work from you, a discriminatory
+patent license (a) in connection with copies of the covered work
+conveyed by you (or copies made from those copies), or (b) primarily
+for and in connection with specific products or compilations that
+contain the covered work, unless you entered into that arrangement,
+or that patent license was granted, prior to 28 March 2007.
+
+  Nothing in this License shall be construed as excluding or limiting
+any implied license or other defenses to infringement that may
+otherwise be available to you under applicable patent law.
+
+  12. No Surrender of Others' Freedom.
+
+  If 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 convey a
+covered work so as to satisfy simultaneously your obligations under this
+License and any other pertinent obligations, then as a consequence you may
+not convey it at all.  For example, if you agree to terms that obligate you
+to collect a royalty for further conveying from those to whom you convey
+the Program, the only way you could satisfy both those terms and this
+License would be to refrain entirely from conveying the Program.
+
+  13. Use with the GNU Affero General Public License.
+
+  Notwithstanding any other provision of this License, you have
+permission to link or combine any covered work with a work licensed
+under version 3 of the GNU Affero General Public License into a single
+combined work, and to convey the resulting work.  The terms of this
+License will continue to apply to the part which is the covered work,
+but the special requirements of the GNU Affero General Public License,
+section 13, concerning interaction through a network will apply to the
+combination as such.
+
+  14. Revised Versions of this License.
+
+  The Free Software Foundation may publish revised and/or new versions of
+the GNU 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 that a certain numbered version of the GNU General
+Public License "or any later version" applies to it, you have the
+option of following the terms and conditions either of that numbered
+version or of any later version published by the Free Software
+Foundation.  If the Program does not specify a version number of the
+GNU General Public License, you may choose any version ever published
+by the Free Software Foundation.
+
+  If the Program specifies that a proxy can decide which future
+versions of the GNU General Public License can be used, that proxy's
+public statement of acceptance of a version permanently authorizes you
+to choose that version for the Program.
+
+  Later license versions may give you additional or different
+permissions.  However, no additional obligations are imposed on any
+author or copyright holder as a result of your choosing to follow a
+later version.
+
+  15. Disclaimer of Warranty.
+
+  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.
+
+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+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.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     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
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    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 3 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, see <http://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program 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, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<http://www.gnu.org/licenses/>.
+
+  The GNU 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.  But first, please read
+<http://www.gnu.org/philosophy/why-not-lgpl.html>.
diff --git a/Makefile b/Makefile
@@ -0,0 +1,36 @@
+PREFIX = /usr/local
+DESTDIR =
+
+LUA_INTERP != ./find_lua
+
+LUA_CFLAGS != pkg-config --cflags $(LUA_INTERP)
+LUA_LDFLAGS != pkg-config --libs $(LUA_INTERP)
+LUA_CMOD_INST != pkg-config --variable=INSTALL_CMOD $(LUA_INTERP)
+
+CFLAGS = -Wall -Wextra -pedantic $(LUA_CFLAGS) -std=c99
+LDFLAGS = $(LUA_LDFLAGS)
+CC = gcc
+
+all: tyarn tyarn.so
+
+tyarn: tyarn.in
+	sed 's|##LUA_INTERP##|$(LUA_INTERP)|' tyarn.in > $@
+
+tyarn.so: tyarn.o
+	$(CC) $(CFLAGS) $(LDFLAGS) -shared -o $@ tyarn.o
+
+tyarn.o: tyarn.c
+	$(CC) -c -fPIC $(CFLAGS) -o $@ tyarn.c
+
+install: all
+	install -D -m 755 tyarn $(DESTDIR)$(PREFIX)/bin/tyarn
+	install -D -m 644 tyarn.so $(DESTDIR)$(LUA_CMOD_INST)/tyarn.so
+
+uninstall: all
+	rm -f $(DESTDIR)$(PREFIX)/bin/tyarn
+	rm -f $(DESTDIR)$(LUA_CMOD_INST)/tyarn.so
+
+clean:
+	rm -f tyarn tyarn.o tyarn.so
+
+.PHONY: uninstall install clean all
diff --git a/README b/README
@@ -0,0 +1,51 @@
+tyarn -- Tiny Yarn
+==================
+
+Cross platform yarn with minimal dependencies.
+
+This is a minimalist yarn[1] by design, it is not as featureful as the original,
+nor does it do any fancy parallel execution like rsyarn[2].
+
+Tested on Debian GNU/Linux and OpenBSD.
+
+Building
+--------
+
+To build tinyyarn you need lua5.1, lua5.1 headers, and pkg-config.
+
+On Debian,
+
+    % apt install lua5.1 liblua5.1-0-dev pkg-config
+
+On OpenBSD,
+
+    % pkg_add lua-5.1.5p6
+
+pkg-config is available in ports.
+
+Then run,
+
+    % make
+
+Installation
+------------
+
+    % make install
+
+Documentation
+-------------
+
+Please see the original yarn project[1] for documentation.
+
+All documentation from the original yarn project should apply,
+however tinyyarn does not support PCREs,
+it uses POSIX extended regular expressions instead.
+
+Contributing
+------------
+
+Please feel welcome to submit patches and bug reports via email,
+using the address found in the git log.
+
+[1]: http://git.liw.fi/cmdtest/
+[2]: https://git.gitano.org.uk/rsyarn.git/
diff --git a/find_lua b/find_lua
@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+
+# stolen from Luxio, credits Rob Kendrick, Daniel Silverstone
+((which lua5.1 > /dev/null 2>&1 && echo lua5.1) ||
+                    (which lua-5.1 > /dev/null 2>&1 && echo lua-5.1) || \
+                    (which lua51  > /dev/null 2>&1 && echo lua51) || \
+                    (lua -e"print(_VERSION)" | grep -q 5.1 && echo lua) || \
+                    (which lua-5.2 > /dev/null 2>&1 && echo lua-5.2) || \
+                    (which lua52 > /dev/null 2>&1 && echo lua52))
diff --git a/tyarn.c b/tyarn.c
@@ -0,0 +1,659 @@
+/* tyarn: minimal yarn implementation
+ *
+ * Copyright © 2019 Richard Ipsum
+ *
+ * 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, version 3 of the License.
+ *
+ * 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, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+/* This program is dedicated to Terry A Davis,
+ * the greatest programmer that ever lived,
+ * may he rest in peace.
+ */
+
+#ifdef __linux__
+#define _XOPEN_SOURCE 500
+#endif
+
+#define _POSIX_C_SOURCE 200809L
+
+#include <lua.h>
+#include <lauxlib.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include <ftw.h>
+#include <sys/types.h>
+#include <sys/select.h>
+#include <regex.h>
+
+struct pipe_state {
+    int fd;
+    char *p;
+    bool eof;
+    char buf[1 * 1024 * 1024];
+};
+
+/* concepts stolen from
+ * https://stackoverflow.com/questions/6137684/iterate-through-lua-table 
+ */
+static const char **arr_from_lua_str_table(lua_State *L, int index, int *len_out)
+{
+    int n = 0;
+    const char **arr = malloc(1 * sizeof (char *));
+    const char **p;
+
+    if (arr == NULL) {
+        return NULL;
+    }
+
+    lua_pushvalue(L, index);
+    lua_pushnil(L);
+
+    while (lua_next(L, -2)) {
+        lua_pushvalue(L, -2);
+
+        lua_tostring(L, -1);
+        const char *value = lua_tostring(L, -2);
+
+        arr[n++] = value;
+
+        p = realloc(arr, (n + 1) * sizeof (char *));
+        if (p == NULL) {
+            free(arr);
+            return NULL;
+        }
+
+        arr = p;
+        lua_pop(L, 2);
+    }
+
+    lua_pop(L, 1);
+
+    arr[n] = NULL;
+    *len_out = n;
+
+    return arr;
+}
+
+static int tyarn_path_exists(lua_State *L)
+{
+    struct stat s;
+    const char *path = luaL_checkstring(L, 1);
+
+    lua_pushboolean(L, (stat(path, &s) == -1 && errno == ENOENT) ? false : true);
+
+    return 1;
+}
+
+static int tyarn_mkdtemp(lua_State *L)
+{
+    const char *path = luaL_checkstring(L, 1);
+    char pathbuf[strlen(path) + 1];
+
+    strncpy(pathbuf, path, sizeof (pathbuf));
+
+    lua_pushstring(L, mkdtemp(pathbuf));
+    lua_pushinteger(L, errno);
+    return 2;
+}
+
+static int tyarn_strerror(lua_State *L)
+{
+    lua_pushstring(L, strerror(luaL_checkinteger(L, -1)));
+    return 1;
+}
+
+static void child_fn(const char **args, const char **env, const char *dir)
+{
+    /* child, do exec */
+    if (dir != NULL && chdir(dir) == -1) {
+        fprintf(stderr, "chdir: %s\n", strerror(errno));
+        exit(1);
+    }
+
+    if (execve(args[0], (char * const *) args, (char * const *) env) == -1) {
+        fprintf(stderr, "exeve: %s\n", strerror(errno));
+        exit(1);
+    }
+}
+
+static int parent_fn(struct pipe_state *stdo, struct pipe_state *stde)
+{
+    fd_set rfds;
+    int maxfds, n, status;
+    struct timeval timeout = {.tv_sec = 1, .tv_usec = 0};
+    struct pipe_state *readers[2] = {stdo, stde};
+    char buf[8192];
+    ssize_t nread;
+    size_t remaining;
+
+    maxfds = readers[0]->fd > readers[1]->fd ? readers[0]->fd : readers[1]->fd;
+
+    for (;;) {
+        FD_ZERO(&rfds);
+        FD_SET(readers[0]->fd, &rfds);
+        FD_SET(readers[1]->fd, &rfds);
+
+        if (readers[0]->eof && readers[1]->eof) {
+            *(readers[0]->p) = '\0';
+            *(readers[1]->p) = '\0';
+            if (wait(&status) == -1) {
+                perror("wait");
+                exit(1);
+            }
+            return status;
+        }
+
+        n = select(maxfds + 1, &rfds, NULL, NULL, &timeout);
+
+        switch (n) {
+            case -1:
+                perror("select");
+                exit(1);
+            case 0:
+                continue;
+            default:
+                for (size_t i = 0; i < 2; i++) {
+                    if (readers[i]->eof || !FD_ISSET(readers[i]->fd, &rfds)) {
+                        continue;
+                    }
+
+                    nread = read(readers[i]->fd, buf, sizeof (buf));
+                    if (nread == -1) {
+                        perror("read");
+                        exit(1);
+                    }
+
+                    if (nread == 0) {
+                        readers[i]->eof = true;
+                        continue;
+                    }
+
+                    remaining = (readers[i]->buf + sizeof (readers[i]->buf)) - readers[i]->p;
+
+                    if ((size_t) nread >= remaining) {
+                        fprintf(stderr, "out of memory\n");
+                        exit(1);
+                    }
+
+                    memcpy(readers[i]->p, buf, nread);
+                    readers[i]->p += nread;
+                }
+        }
+     }
+}
+
+static int tyarn_exec(lua_State *L)
+{
+    int args_len, env_len;
+    int status;
+    const char **args, **env;
+    const char *dir;
+    int stdout_pipefds[2];
+    int stderr_pipefds[2];
+    struct pipe_state stdo = {0, .eof = false};
+    struct pipe_state stde = {0, .eof = false};
+    stdo.p = stdo.buf;
+    stde.p = stde.buf;
+
+    luaL_checktype(L, 1, LUA_TTABLE);
+    luaL_checktype(L, 2, LUA_TTABLE);
+    dir = luaL_checkstring(L, 3);
+
+    args = arr_from_lua_str_table(L, 1, &args_len);
+    if (args == NULL) {
+        lua_pushinteger(L, -1);
+        lua_pushinteger(L, EINVAL);
+        return 2;
+    }
+
+    env = arr_from_lua_str_table(L, 2, &env_len);
+    if (env == NULL) {
+        lua_pushinteger(L, -1);
+        lua_pushinteger(L, EINVAL);
+        return 2;
+    }
+
+    if (pipe(stdout_pipefds) == -1) {
+        perror("pipe");
+        exit(1);
+    }
+
+    if (pipe(stderr_pipefds) == -1) {
+        perror("pipe");
+        exit(1);
+    }
+
+    switch (fork()) {
+        case 0:
+            close(STDOUT_FILENO);
+            if (dup(stdout_pipefds[1]) == -1) {
+                perror("dup");
+                exit(1);
+            }
+
+            close(STDERR_FILENO);
+            if (dup(stderr_pipefds[1]) == -1) {
+                perror("dup");
+                exit(1);
+            }
+
+            /* close read ends */
+            close(stdout_pipefds[0]);
+            close(stderr_pipefds[0]);
+
+            /* close left over descriptors
+             * no longer needed now they've been dup'd to stdout and stderr
+             */
+            close(stdout_pipefds[1]);
+            close(stderr_pipefds[1]);
+
+            /* child, do the work */
+            child_fn(args, env, dir);
+            break;
+        case -1:
+            perror("fork");
+            exit(1);
+        default:
+            close(stdout_pipefds[1]);
+            close(stderr_pipefds[1]);
+            stdo.fd = stdout_pipefds[0];
+            stde.fd = stderr_pipefds[0];
+
+            /* parent, wait for child to complete */
+            status = parent_fn(&stdo, &stde);
+
+            close(stdo.fd);
+            close(stde.fd);
+
+            lua_pushinteger(L, 0);
+            lua_pushinteger(L, WEXITSTATUS(status));
+            lua_pushstring(L, stdo.buf);
+            lua_pushstring(L, stde.buf);
+            return 4;
+    }
+
+    return 0;
+}
+
+static int remove_entry(const char *name, const struct stat *s, int flag, struct FTW *f)
+{
+    (void) flag;
+    (void) f;
+
+    if (S_ISDIR(s->st_mode)) {
+        if (rmdir(name) == -1) {
+            fprintf(stderr, "rmdir: %s\n", strerror(errno));
+            return 1;
+        }
+
+        return 0;
+    }
+
+    if (unlink(name) == -1) {
+        fprintf(stderr, "unlink: %s\n", strerror(errno));
+        return 1;
+    }
+
+    return 0;
+}
+
+static int tyarn_rmutil(lua_State *L)
+{
+    const char *dir = luaL_checkstring(L, -1);
+
+    if (nftw(dir, remove_entry, 100, FTW_DEPTH | FTW_MOUNT | FTW_PHYS) == -1) {
+        fprintf(stderr, "Error traversing %s\n", dir);
+        exit(1);
+    }
+
+    return 0;
+}
+
+static void usage(void)
+{
+    fprintf(stderr, "usage: tyarn [-CdEehlstv] SCENARIO_FILE IMPLEMENTATION_FILE\n");
+}
+
+static int tyarn_usage(lua_State *L)
+{
+    (void) L;
+
+    usage();
+    return 0;
+}
+
+static void help(void)
+{
+    usage();
+
+    const char *s = "\nOptions:\n"
+        "  -C       Don't cleanup temporary files and directories\n"
+        "  -d       Enable debug\n"
+        "  -E       Exit early (exit when first scenario fails)\n"
+        "  -e NAME=VALUE\n"
+        "           Add an environment variable to the test's environment\n"
+        "           (this argument can be repeated to add multiple variables)\n"
+        "  -h       This help message\n"
+        "  -l SHELL_LIBRARY\n"
+        "           Shell library to be used by scenario implementations\n"
+        "  -s SHELL Execute scenario implementations using SHELL\n"
+        "  -t DIR\n"
+        "           Use DIR as temporary directory for tests\n"
+        "           DIR is a template e.g. /tmp/foo.XXXXXXXX\n"
+        "           There must be at least six trailing Xs\n"
+        "  -v       Verbose\n";
+
+    fprintf(stderr, s);
+}
+
+static int tyarn_help(lua_State *L)
+{
+    (void) L;
+
+    help();
+    return 0;
+}
+
+static int tyarn_parse_args(lua_State *L)
+{
+    const char **args;
+    int args_len;
+    int c = 42;
+    char *shell_lib = NULL;
+    char **buf;
+    bool debug = false;
+    bool no_cleanup = false;
+    bool exit_early = false;
+    bool help = false;
+    int verbose = 0;
+    char *tmpdir = NULL;
+    char *shell = NULL;
+    char *envopts[8192];
+    size_t envoptsn = 0;
+
+    luaL_checktype(L, 1, LUA_TTABLE);
+
+    args = arr_from_lua_str_table(L, 1, &args_len);
+    if (args == NULL) {
+        lua_pushinteger(L, -1);
+        lua_pushinteger(L, EINVAL);
+        return 2;
+    }
+
+    buf = malloc(args_len * sizeof (char *));
+    if (buf == NULL) {
+        fprintf(stderr, "out of memory\n");
+        exit(1);
+    }
+
+    int bufn = 0;
+    buf[bufn++] = strdup("tyarn");
+
+    for (int i = 0; i < args_len - 2; i++) {
+        buf[bufn++] = strdup(args[i]);
+    }
+
+    while ((c = getopt(bufn, buf, ":l:s:dECht:e:v")) != -1) {
+        switch (c) {
+            case 'C':
+                no_cleanup = true;
+                break;
+            case 'E':
+                exit_early = true;
+                break;
+            case 'e':
+                envopts[envoptsn++] = optarg;
+                break;
+            case 'l':
+                shell_lib = optarg;
+                break;
+            case 's':
+                shell = optarg;
+                break;
+            case 'd':
+                debug = true;
+                break;
+            case 'h':
+                help = true;
+                break;
+            case 'v':
+                verbose++;
+                break;
+            case 't':
+                tmpdir = optarg;
+                break;
+            case ':':
+                fprintf(stderr, "%s: missing option\n", buf[0]);
+                exit(1);
+            default:
+                usage();
+                exit(1);
+        }
+    }
+
+    lua_createtable(L, bufn - optind, optind);
+    lua_pushstring(L, shell_lib);
+    lua_setfield(L, -2, "shell_lib");
+    lua_pushboolean(L, debug);
+    lua_setfield(L, -2, "debug");
+    lua_pushboolean(L, no_cleanup);
+    lua_setfield(L, -2, "no_cleanup");
+    lua_pushboolean(L, exit_early);
+    lua_setfield(L, -2, "exit_early");
+    lua_pushboolean(L, help);
+    lua_setfield(L, -2, "help");
+    lua_pushstring(L, tmpdir);
+    lua_setfield(L, -2, "tmpdir");
+    lua_pushinteger(L, verbose);
+    lua_setfield(L, -2, "verbose");
+    lua_pushstring(L, shell);
+    lua_setfield(L, -2, "shell");
+
+    int tn = 1;
+    for (int i = optind; i < bufn; i++) {
+        lua_pushstring(L, buf[i]);
+        lua_rawseti(L, -2, tn++);
+    }
+
+    lua_createtable(L, 0, envoptsn);
+
+    for (size_t i = 0; i < envoptsn; i++) {
+        lua_pushstring(L, envopts[i]);
+        lua_rawseti(L, -2, i + 1);
+    }
+
+    for (int i = 0; i < bufn; i++) {
+        free(buf[i]);
+    }
+    free(buf);
+    return 2;
+}
+
+static int tyarn_unlink(lua_State *L)
+{
+    lua_pushinteger(L, unlink(luaL_checkstring(L, 1)));
+    lua_pushinteger(L, errno);
+    return 2;
+}
+
+static int tyarn_mkstemp(lua_State *L)
+{
+    const char *path = luaL_checkstring(L, 1);
+    char template[strlen(path) + 1];
+    strncpy(template, path, sizeof (template));
+    int fd = mkstemp(template);
+
+    if (fd == -1) {
+        lua_pushnil(L);
+        lua_pushstring(L, strerror(errno));
+        return 2;
+    }
+
+    close(fd);
+    /* this is super lame, a nicer way would be to make a luaStream,
+     * http://lua-users.org/lists/lua-l/2014-11/msg00120.html, not supported in 5.1 though
+     */
+
+    lua_pushstring(L, template);
+    return 1;
+}
+
+static char *str_from_offs(const char *orig, regoff_t start, regoff_t end)
+{
+    char buf[strlen(orig) + 1];
+    char *p;
+    strncpy(buf, orig, sizeof (buf));
+
+    p = buf + start;
+    buf[end] = '\0';
+
+    return strdup(p);
+}
+
+static int tyarn_rematch(lua_State *L)
+{
+    const char *string = luaL_checkstring(L, 1);
+    const char *pattern = luaL_checkstring(L, 2);
+    int ret;
+    regex_t r = {.re_nsub = 0};
+    regmatch_t pmatch[100];
+    char errstr[8192];
+
+    ret = regcomp(&r, pattern, REG_EXTENDED);
+    if (ret != 0) {
+        regerror(ret, &r, errstr, sizeof (errstr));
+        lua_pushnil(L);
+        lua_pushstring(L, errstr);
+        return 2;
+    }
+
+    ret = regexec(&r, string, 100, pmatch, 0);
+    if (ret != 0) {
+        regerror(ret, &r, errstr, sizeof (errstr));
+        lua_pushnil(L);
+        lua_pushstring(L, errstr);
+        return 2;
+    }
+
+    lua_pushinteger(L, 1);
+
+    lua_createtable(L, r.re_nsub, 0);
+    int tn = 1;
+    for (size_t i = 1; i <= r.re_nsub; i++) {
+        char *s = str_from_offs(string, pmatch[i].rm_so, pmatch[i].rm_eo); 
+        lua_pushstring(L, s);
+        lua_rawseti(L, -2, tn++);
+        free(s);
+    }
+
+    return 2;
+}
+
+static int tyarn_refind(lua_State *L)
+{
+    const char *string = luaL_checkstring(L, 1);
+    const char *pattern = luaL_checkstring(L, 2);
+    int ret;
+    regex_t r = {.re_nsub = 0};
+    regmatch_t pmatch[100];
+    char errstr[8192];
+    const char *p = string;
+    bool match = false;
+
+    ret = regcomp(&r, pattern, REG_EXTENDED);
+    if (ret != 0) {
+        regerror(ret, &r, errstr, sizeof (errstr));
+        lua_pushnil(L);
+        lua_pushstring(L, errstr);
+        return 2;
+    }
+
+    while (*p != '\0') {
+        ret = regexec(&r, p, 100, pmatch, 0);
+
+        switch (ret) {
+            case REG_NOMATCH:
+                p++;
+                continue;
+            case 0:
+                match = true;
+                goto out;
+            default:
+                regerror(ret, &r, errstr, sizeof (errstr));
+                lua_pushnil(L);
+                lua_pushstring(L, errstr);
+                return 2;
+        }
+    }
+
+out:
+    if (!match) {
+        lua_pushnil(L);
+        lua_pushnil(L);
+        return 2;
+    }
+
+    lua_pushinteger(L, 1);
+    lua_createtable(L, r.re_nsub, 0);
+    int tn = 1;
+    for (size_t i = 1; i <= r.re_nsub; i++) {
+        char *s = str_from_offs(p, pmatch[i].rm_so, pmatch[i].rm_eo);
+        lua_pushstring(L, s);
+        lua_rawseti(L, -2, tn++);
+        free(s);
+    }
+
+    return 2;
+}
+
+static int tyarn_mkdir(lua_State *L)
+{
+    const char *path = luaL_checkstring(L, 1);
+
+    lua_pushinteger(L, mkdir(path, S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH));
+    lua_pushstring(L, strerror(errno));
+
+    return 2;
+}
+
+static const struct luaL_Reg tyarn_functions[] = {
+    {"exec", tyarn_exec},
+    {"mkdtemp", tyarn_mkdtemp},
+    {"strerror", tyarn_strerror},
+    {"rmutil", tyarn_rmutil},
+    {"parse_args", tyarn_parse_args},
+    {"unlink", tyarn_unlink},
+    {"mkstemp", tyarn_mkstemp},
+    {"re_match", tyarn_rematch},
+    {"re_find", tyarn_refind},
+    {"usage", tyarn_usage},
+    {"help", tyarn_help},
+    {"path_exists", tyarn_path_exists},
+    {"mkdir", tyarn_mkdir},
+    {NULL, NULL}
+};
+
+int luaopen_tyarn(lua_State *L)
+{
+    luaL_register(L, "tyarn", tyarn_functions);
+    return 1;
+}
+
diff --git a/tyarn.in b/tyarn.in
@@ -0,0 +1,434 @@
+#!/usr/bin/env ##LUA_INTERP##
+--
+-- Copyright © 2019 Richard Ipsum
+--
+-- 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, version 3 of the License.
+--
+-- 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, see <http://www.gnu.org/licenses/>.
+--
+
+local tyarn = require 'tyarn'
+
+local scenario_env = {}
+local parsed_args = {}
+local parsed_env = {}
+
+local DEBUG = nil
+local DEFAULT_SHELL = "sh"
+
+function debug(...)
+    if parsed_args["debug"] or DEBUG then
+        print(...)
+    end
+end
+
+function lstrip(s)
+    return string.gsub(s, '%s+', '', 1)
+end
+
+function parse_implementations(filepath)
+    implementations = {}
+
+    file, err = io.open(filepath)
+    if file == nil then
+        io.stderr:write(string.format("Couldn't open implementation file: %s\n", filepath, err))
+        os.exit(1)
+    end
+
+    for line in file:lines() do
+        -- ignore lines that are not indented or blank
+        matched, matches = tyarn.re_match(line, "^(    )+[^ \t\n\r\f\v]+")
+        line = lstrip(line)
+
+        if matched then
+            if string.find(line, "IMPLEMENTS") then
+                key = string.gsub(line, "IMPLEMENTS%s+", "")
+                implementations[key] = {}
+            elseif key ~= nil then
+                -- in the middle of a step's implementation
+                --print(string.format('debug: %s', string.gsub(key, "IMPLEMENTS%s+", "")))
+                table.insert(implementations[key], line)
+            end
+        end
+    end
+
+    return implementations
+end
+
+function validate_scenario(steps_seen, scenario_name, scenario_line_no)
+    if not steps_seen["WHEN"] then
+        io.stderr:write(string.format('Scenario "%s" (line %d) has no WHEN step\n',
+                                      scenario_name, scenario_line_no))
+        os.exit(1)
+    end
+
+    if not steps_seen["THEN"] then
+        io.stderr:write(string.format('Scenario "%s" (line %d) has no THEN step\n',
+                                      scenario_name, scenario_line_no))
+        os.exit(1)
+    end
+end
+
+function parse_scenario_line(scenario, scenario_name, steps_seen,
+                             line, line_no, last_step_type)
+    stripped_line = lstrip(line)
+
+    if tyarn.re_match(line, "^(    )[ \t]*GIVEN") then
+        table.insert(scenario, stripped_line)
+        last_step_type = "GIVEN"
+        steps_seen["GIVEN"] = true
+    elseif tyarn.re_match(line, "^(    )[ \t]*WHEN") then
+        table.insert(scenario, stripped_line)
+        last_step_type = "WHEN"
+        steps_seen["WHEN"] = true
+    elseif tyarn.re_match(line, "^(    )[ \t]*THEN") then
+        table.insert(scenario, stripped_line)
+        last_step_type = "THEN"
+        steps_seen["THEN"] = true
+    elseif tyarn.re_match(line, "^(    )[ \t]*ASSUMING") then
+        table.insert(scenario, stripped_line)
+        last_step_type = "ASSUMING"
+        steps_seen["ASSUMING"] = true
+    elseif tyarn.re_match(line, "^(    )[ \t]*AND") then
+        if last_step_type == nil then
+            io.stderr:write(string.format(
+                'Scenario "%s" (line %d) has AND as first step: %s\n',
+                scenario_name, line_no, stripped_line))
+            os.exit(1)
+        end
+
+        processed_line = string.gsub(stripped_line, "AND", last_step_type)
+
+        if last_step_type == "FINALLY" then
+            table.insert(scenario["FINALLY"], processed_line)
+        else
+            table.insert(scenario, processed_line)
+        end
+    elseif tyarn.re_match(line, "^(    )[ \t]*FINALLY") then
+        last_step_type = "FINALLY"
+        steps_seen["FINALLY"] = true
+        table.insert(scenario["FINALLY"], stripped_line)
+    end
+
+    return last_step_type
+end
+
+function _parse_scenarios(scenarios, file, scenario_name, scenario_line_no)
+    debug('Parsing scenario', scenario_name)
+    last_step_type = nil
+    scenario = {}
+    scenario["FINALLY"] = {}
+    line_no = scenario_line_no
+    steps_seen = {}
+    in_scenario = true
+
+    for line in file:lines() do
+        line_no = line_no + 1
+
+        if string.len(line) == 0 then
+            -- blank line
+            in_scenario = false
+        end
+
+        if in_scenario then
+            last_step_type = parse_scenario_line(scenario, scenario_name, steps_seen,
+                                                 line, line_no, last_step_type)
+        end
+
+        -- ignore lines that aren't indented by one level
+        matched, matches = tyarn.re_match(line, "^(    )SCENARIO ([^ \t\n\r\f\v]+.*)")
+
+        if matched then
+            -- we've hit the end of the current scenario
+            -- validate, and store current scenario
+            validate_scenario(steps_seen, scenario_name, scenario_line_no)
+            scenarios[scenario_name] = scenario
+
+            -- now onto the next scenario
+            scenario_name = matches[2]
+            _parse_scenarios(scenarios, file, scenario_name, line_no)
+            return
+        end
+    end
+
+    -- hit the end of the file, validate the current scenario
+    -- assuming there is a current scenario
+    if scenario_name then
+        validate_scenario(steps_seen, scenario_name, scenario_line_no)
+        scenarios[scenario_name] = scenario
+    end
+end
+
+function parse_scenarios(filepath)
+    scenarios = {}
+    line_no = 0
+
+    file, err = io.open(filepath)
+    if file == nil then
+        io.stderr:write(string.format("Couldn't open scenario file: %s\n", err))
+        os.exit(1)
+    end
+
+    -- parse the first scenario line, as the base case
+    for line in file:lines() do
+        line_no = line_no + 1
+
+        matched, matches = tyarn.re_match(line, "^(    )SCENARIO ([^ \t\n\r\f\v]+.*)")
+
+        if matched then
+            scenario_name = matches[2]
+            break
+        end
+    end
+
+    -- now we have the base case, begin the recursion
+    _parse_scenarios(scenarios, file, scenario_name, line_no)
+
+    return scenarios
+end
+
+function find_matching_implementation(implementations, step)
+    for patt, impl in pairs(implementations) do
+
+        matched, matches = tyarn.re_find(step, patt)
+        if matched then
+            return impl, matches
+        end
+    end
+
+    return nil, nil
+end
+
+function load_shell_library(path)
+    fh, err = io.open(path)
+
+    if fh == nil then
+        io.stderr:write(string.format("tyarn: Couldn't open shell library: %s\n", err))
+        os.exit(1)
+    end
+
+    return fh:read('*all')
+end
+
+function run_step(scenario_dir, datadir, implementations, scenario_key, step, shell_prelude)
+    success = true
+    skip_scenario = false
+    env = {}
+    shell_script_lines = {}
+    table.insert(env, string.format("DATADIR=%s", datadir))
+    debug(string.format(string.format("Run step %s", step)))
+
+    step_impl, step_captures = find_matching_implementation(implementations, step)
+    if step_impl == nil then
+        error(string.format("No matching implementations for step '%s'", step))
+    end
+
+    for _, capture in pairs(step_captures) do
+        debug(string.format("capture: %s", capture))
+    end
+
+    for n, capture in ipairs(step_captures) do
+        table.insert(env, string.format('MATCH_%d=%s', n, capture))
+    end
+
+    for k, v in pairs(parsed_env) do
+        table.insert(env, v)
+    end
+
+    for _, impl_line in ipairs(step_impl) do
+        debug('impl_line', impl_line)
+        table.insert(shell_script_lines, impl_line)
+    end
+
+    shell_script_str = table.concat(shell_script_lines, '\n')
+    path, err = tyarn.mkstemp(string.format("%s/%s", scenario_dir, "tyarn_shell_script.XXXXXXX"))
+    if path == nil then
+        io.stderr:write(string.format("tyarn: Error creating shell script: %s\n", err))
+        os.exit(1)
+    end
+
+    debug("datadir:", datadir)
+    debug("path:", path)
+
+    shell_script, err = io.open(path, "w")
+    if shell_script == nil then
+        io.stderr:write(string.format("tyarn: Couldn't open implementation shell script: %s\n", err))
+        os.exit(1)
+    end
+
+    shell_script:write(shell_prelude)
+    shell_script:write(shell_script_str)
+    shell_script:close()
+    debug('shell_script_str:', shell_script_str)
+
+    cmd = {"/usr/bin/env", parsed_args["shell"] or DEFAULT_SHELL, path}
+    ret, exit_code, stdout, stderr = tyarn.exec(cmd, env, datadir)
+    debug('ret', ret, 'exit_code', exit_code)
+    if ret == -1 then
+        error(string.format("Failed to exec step: %s", impl_step))
+    end
+
+    if parsed_args["debug"] then
+        print(string.format("Logging stdout from shell command:\n%s\n", stdout))
+        print(string.format("Logging stderr from shell command:\n%s\n", stderr))
+    end
+
+    if exit_code ~= 0 then
+        if string.sub(step, 1, string.len("ASSUMING")) == "ASSUMING" then
+            io.stderr:write(string.format('Skipping "%s" because "%s" failed\n', scenario_key, step))
+            skip_scenario = true
+        else
+            io.stderr:write(string.format('ERROR: In scenario: "%s" ', scenario_key))
+            io.stderr:write(string.format('step "%s" failed with exit code %d\n', step, exit_code))
+            io.stderr:write(string.format("Standard output from shell command:\n%s\n", stdout))
+            io.stderr:write(string.format("Standard error from shell command:\n%s\n", stderr))
+
+            success = false
+        end
+    end
+
+    if not parsed_args["no_cleanup"] then
+        tyarn.unlink(path)
+    end
+
+    return success, skip_scenario
+end
+
+function fs_quote(s)
+    -- Make string more nicely represented as a path
+    -- Replace ' ' with '_', and lower case the entire string.
+
+    -- FIXME: potential bug here, multiple scenario keys can map to the same path!
+    -- e.g. scenario_key /okay/ and (okay) both map to _okay_
+    return s:gsub("[ /'\"()]", "_"):lower()
+end
+
+function run_scenario(scenarios, implementations, scenario_key, shell_lib_path)
+    print('Running', scenario_key)
+    scenario = scenarios[scenario_key]
+    tmpdir = nil
+
+    debug('parsed_args["tmpdir"]', parsed_args["tmpdir"])
+
+    if parsed_args["tmpdir"] ~= nil then
+        debug('path exists?', tyarn.path_exists(parsed_args["tmpdir"]))
+        if tyarn.path_exists(parsed_args["tmpdir"]) then
+            tmpdir = parsed_args["tmpdir"]
+        else
+            tmpdir, errno = tyarn.mkdtemp(parsed_args["tmpdir"])
+        end
+    else
+        tmpdir, errno = tyarn.mkdtemp("/tmp/temp.XXXXXX")
+    end
+
+    debug('tmpdir', tmpdir)
+
+    scenario_fs_key = fs_quote(scenario_key)
+
+    if shell_lib_path then
+        shell_prelude = load_shell_library(shell_lib_path)
+        debug('shell_prelude', shell_prelude)
+    else
+        shell_prelude = ''
+    end
+
+    if tmpdir == nil then
+        if errno == nil then
+            errmsg = "???"
+        else
+            errmsg = tyarn.strerror(errno)
+        end
+        io.stderr:write(string.format("Failed to make tmpdir: %s\n", errmsg))
+        os.exit(1)
+    end
+
+    scenario_dir = string.format("%s/%s", tmpdir, scenario_fs_key)
+    ret, err = tyarn.mkdir(scenario_dir)
+    if ret == -1 then
+        io.stderr:write(string.format('tyarn: mkdir "%s" failed: %s\n', scenario_dir, err))
+        os.exit(1)
+    end
+
+    datadir = string.format("%s/DATADIR", scenario_dir)
+    ret, err = tyarn.mkdir(datadir)
+    if ret == -1 then
+        io.stderr:write(string.format('tyarn: mkdir "%s" failed: %s\n', datadir, err))
+        os.exit(1)
+    end
+
+    for n, step in ipairs(scenario) do
+        if parsed_args['verbose'] > 0 then
+            print('Running step', step)
+        end
+        success, skip_scenario = run_step(scenario_dir, datadir, implementations,
+                                          scenario_key, step, shell_prelude)
+
+        if not success then
+            -- run FINALLY steps, if any
+            for _, step in pairs(scenario["FINALLY"]) do
+                success, _ = run_step(scenario_dir, datadir, implementations,
+                                      scenario_key, step, shell_prelude)
+            end
+
+            if parsed_args["exit_early"] then
+                os.exit(1)
+            end
+
+            break
+        end
+
+        if skip_scenario then
+            -- ASSUME step failed, skip the rest of the steps in the scenario
+            break
+        end
+    end
+
+    if not parsed_args["no_cleanup"] then
+        tyarn.rmutil(datadir)
+    end
+end
+
+parsed_args, parsed_env = tyarn.parse_args(arg)
+
+if parsed_args["help"] then
+    tyarn.help()
+    os.exit(0)
+end
+
+if #parsed_args < 2 then
+    tyarn.usage()
+    os.exit(0)
+end
+
+if parsed_args["debug"] or DEBUG then
+    print("Args:")
+    for k, v in ipairs(parsed_args) do
+        print(k, v)
+    end
+
+    print("Parsed environment options:")
+    for k, v in pairs(parsed_env) do
+        print(k, v)
+    end
+end
+
+scenarios = parse_scenarios(parsed_args[1])
+implementations = parse_implementations(parsed_args[2])
+
+for k,v in pairs(scenarios) do
+    run_scenario(scenarios, implementations, k, parsed_args['shell_lib'])
+    seen_scenario = true
+end
+
+if not seen_scenario then
+    io.stderr:write("No scenarios\n")
+    os.exit(1)
+end