MDL (programming language)

{{Short description|Lisp-like programming language}} {{Infobox programming language | name = MDL | logo =  | logo caption = | screenshot =  | screenshot caption = | paradigms = Multi-paradigm: functional, procedural, reflective, meta | family = Lisp | designers = Gerald Sussman, Carl Hewitt, Chris Reeve, Bruce Daniels | developer = MIT Project MAC | released = {{Start date and age|1971}} | latest release version = 105 | latest release date = {{Start date and age|1980}} | typing = Dynamic, strong | scope = Static, lexical | programming language = MDL | discontinued = Yes | platform = PDP-10, VAX, Apollo/Domain | operating system = ITS, TENEX, TOPS-20, BSD, AEGIS | license = Open-source | file ext = | file format =  | website =  | implementations = | dialects = | influenced by = Lisp | influenced = ZIL, Planner, Scheme, Common Lisp, Java, Prolog, Smalltalk; actor model, interactive fiction }} '''MDL''' ('''Model Development Language''',<ref name="Supnik2006">{{cite interview |last1=Supnik |first1=Bob |interviewer=Jason Scott |title=GET LAMP Bob Supnik Interview |date=October 25, 2006 |url=https://archive.org/details/GETLAMP-Supnik |at=15:00}}</ref> or colloquially also referred to as '''More Datatypes than Lisp'''<ref name="Licklider1988"> {{cite report |last1=Licklider |first1=J. C. R. |author1-link=J. C. R. Licklider |date=January 1988 |url=https://apps.dtic.mil/dtic/tr/fulltext/u2/a197342.pdf |title=Graphical Programming and Monitoring RADC-TR-88-7 |publisher=Rome Air Development Center |url-status=live |archive-url=https://web.archive.org/web/20190503021117/https://apps.dtic.mil/dtic/tr/fulltext/u2/a197342.pdf |archive-date=May 3, 2019 |access-date=2019-05-18}}</ref>{{rp|3}} or '''MIT Design Language'''{{citation needed|date=May 2019}}) is a programming language, a descendant of the language Lisp. Its initial purpose was to provide high-level programming language support for the Dynamic Modeling Group at Massachusetts Institute of Technology's (MIT) Project MAC.<ref name="DornbrookBlank"> {{cite book |last1=Dornbrook |first1=Michael |last2=Blank |first2=Marc |date=1980 |url=http://publications.csail.mit.edu/lcs/pubs/pdf/MIT-LCS-TR-292.pdf |title=MDL Programming Primer MIT-LCS-TR-292 |publisher=Massachusetts Institute of Technology, Laboratory for Computer Science |access-date=2019-05-18}}</ref> It was developed in 1971 on a PDP-10 running ITS and later ran on TENEX, TOPS-20,<ref name="GalleyPfister1979"> {{cite book |last1=Galley |first1=Stu W. |last2=Pfister |first2=Greg |date=1979 |url=http://ifarchive.org/if-archive/programming/mdl/manuals/MDL_Programming_Language.pdf |title=The MDL Programming Language |publisher=Massachusetts Institute of Technology, Laboratory for Computer Science |access-date=2018-12-18}} ([https://mdl-language.readthedocs.io/en/latest/ Markdown/HTML transcription])</ref><ref> {{cite book |last1=Lebling |first1=P. David |date=May 1980 |url=http://ifarchive.org/if-archive/programming/mdl/manuals/MDL_Programming_Environment.pdf |title=The MDL Programming Environment |publisher=Massachusetts Institute of Technology, Laboratory for Computer Science |access-date=2018-12-18}}</ref> BSD,<ref name="Licklider1988"/>{{rp|6}} and AEGIS.<ref name="Lim1982"> {{cite report |last1=Lim |first1=Poh Chuan |date=1982 |url=https://dspace.mit.edu/bitstream/handle/1721.1/102210/10219781-MIT.pdf#page=69 |title=A Device-Independent Graphics Manager for MDL |page=69 |publisher=Massachusetts Institute of Technology |access-date=2019-05-18}}</ref>

The initial development team consisted of Gerald Sussman and Carl Hewitt of the Artificial Intelligence Lab, and Chris Reeve, Bruce Daniels, and David Cressey of the Dynamic Modeling Group. Later, Stu Galley, also of the Dynamic Modeling Group, wrote the MDL documentation.{{citation needed|date=August 2013}}

MDL was initially called ''Muddle''.<ref name="GalleyPfister1979"/>{{rp|2}} This style of self-deprecating humor was not widely understood or appreciated outside of Project MAC. So the name was sanitized to MDL.{{citation needed|date=May 2013}}

MDL provides several enhancements to classic Lisp. It supports several built-in data types, including lists, strings and arrays, and user-defined data types. It offers multithreaded expression evaluation and coroutines. Variables can carry both a local value within a scope, and a global value, for passing data between scopes. Advanced built-in functions supported interactive debugging of MDL programs, incremental development, and reconstruction of source programs from object programs.

Although MDL is obsolete, some of its features have been incorporated in later versions of Lisp. Gerald Sussman went on to develop the Scheme language, in collaboration with Guy Steele, who later wrote the specifications for Common Lisp and Java. Carl Hewitt had already published the idea for the language ''Planner'' before the MDL project began, but his subsequent thinking on Planner reflected lessons learned from building MDL. Planner concepts influenced languages such as Prolog and Smalltalk. Smalltalk and Simula, in turn, influenced Hewitt's future work on the actor model.

But the largest influence that MDL had was on the software genre of interactive fiction (IF). An IF game named Zork, sometimes called Dungeon, was first written in MDL.<ref name="dyer19840506">{{Cite news |last1=Dyer |first1=Richard |date=1984-05-06 |url=http://www.csd.uwo.ca/Infocom/Articles/globe84.html |title=Masters of the Game |newspaper=The Boston Globe |url-status=dead |archive-url=https://web.archive.org/web/19970607204921/http://www.csd.uwo.ca/Infocom/Articles/globe84.html |archive-date=1997-06-07}}</ref> Later, Reeve, Daniels, Galley and other members of Dynamic Modeling went on to start Infocom, a company that produced many early commercial works of interactive fiction.

In 1980 Marc Blank and Joel Berez adapted the MDL language to create a subset called ZIL (Zork Implementation Language) which was used extensively by Infocom to create their award winning games.

==Code sample== This is a sample of PDP-10 MDL:<ref>{{cite web |url=http://simh.trailing-edge.com/games/zork-mdl.zip |title=Zork-mdl.zip}}</ref><ref>{{cite web |url=http://simh.trailing-edge.com/software.html |title=Software Kits |last1=Supnik |first1=Bob |date=2018-06-04 |website=Computer Simulation and History (SimH) |publisher=Bitsavers.org |access-date=2018-12-18}}</ref><ref>{{cite web |url=http://pdp-11.ru/simh_trailing-edge_com/software.html |title=Software Kits |last1=Supnik |first1=Bob |date=2007-09-02 |website=Computer Simulation and History (SimH) |publisher=Forum PDP-11 |access-date=2018-12-18}}</ref>

<syntaxhighlight lang="clojure"> <DEFINE EXIT-TO (EXITS RMS) #DECL ((EXITS) EXIT (RMS) <UVECTOR [REST ROOM]>) <MAPF <> <FUNCTION (E) #DECL ((E) <OR DIRECTION ROOM CEXIT NEXIT DOOR>) <COND (<TYPE? .E DIRECTION>) (<AND <TYPE? .E ROOM> <MEMQ .E .RMS>> <MAPLEAVE T>) (<AND <TYPE? .E CEXIT> <MEMQ <2 .E> .RMS>> <MAPLEAVE T>) (<AND <TYPE? .E DOOR> <OR <MEMQ <DROOM1 .E> .RMS> <MEMQ <DROOM2 .E> .RMS>>> <MAPLEAVE T>)>> .EXITS>> </syntaxhighlight>

==References== {{Reflist}}

==External links==

{{DEFAULTSORT:Mdl (Programming Language)}} Category:Dynamically typed programming languages Category:Functional languages Category:Lisp programming language family  Category:Articles with example Lisp (programming language) code