MDL (Model Development Language, or colloquially also referred to as More Datatypes than Lisp or MIT Design Language) is a

programming language A programming language is a system of notation for writing computer programs. Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually def ...

, a descendant of the language

Lisp Lisp (historically LISP, an abbreviation of "list processing") is a family of programming languages with a long history and a distinctive, fully parenthesized Polish notation#Explanation, prefix notation. Originally specified in the late 1950s, ...

. Its initial purpose was to provide

high-level programming language A high-level programming language is a programming language with strong Abstraction (computer science), abstraction from the details of the computer. In contrast to low-level programming languages, it may use natural language ''elements'', be ea ...

support for the Dynamic Modeling Group at

Massachusetts Institute of Technology The Massachusetts Institute of Technology (MIT) is a Private university, private research university in Cambridge, Massachusetts, United States. Established in 1861, MIT has played a significant role in the development of many areas of moder ...

's (MIT) Project MAC. It was developed in 1971 on a

PDP-10 Digital Equipment Corporation (DEC)'s PDP-10, later marketed as the DECsystem-10, is a mainframe computer family manufactured beginning in 1966 and discontinued in 1983. 1970s models and beyond were marketed under the DECsystem-10 name, especi ...

running ITS and later ran on TENEX, TOPS-20,
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BSD, and AEGIS. 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. MDL was initially called ''Muddle''. This style of self-deprecating humor was not widely understood or appreciated outside of Project MAC. So the name was sanitized to MDL. 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

coroutine Coroutines are computer program components that allow execution to be suspended and resumed, generalizing subroutines for cooperative multitasking. Coroutines are well-suited for implementing familiar program components such as cooperative task ...

s. 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 In engineering, debugging is the process of finding the Root cause analysis, root cause, workarounds, and possible fixes for bug (engineering), bugs. For software, debugging tactics can involve interactive debugging, control flow analysis, Logf ...

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 Common Lisp (CL) is a dialect of the Lisp programming language, published in American National Standards Institute (ANSI) standard document ''ANSI INCITS 226-1994 (S2018)'' (formerly ''X3.226-1994 (R1999)''). The Common Lisp HyperSpec, a hyperli ...

and

Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...

. 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 Prolog is a logic programming language that has its origins in artificial intelligence, automated theorem proving, and computational linguistics. Prolog has its roots in first-order logic, a formal logic. Unlike many other programming language ...

and

Smalltalk Smalltalk is a purely object oriented programming language (OOP) that was originally created in the 1970s for educational use, specifically for constructionist learning, but later found use in business. It was created at Xerox PARC by Learni ...

. Smalltalk and

Simula Simula is the name of two simulation programming languages, Simula I and Simula 67, developed in the 1960s at the Norwegian Computing Center in Oslo, by Ole-Johan Dahl and Kristen Nygaard. Syntactically, it is an approximate superset of AL ...

, in turn, influenced Hewitt's future work on the

actor model The actor model in computer science is a mathematical model of concurrent computation that treats an ''actor'' as the basic building block of concurrent computation. In response to a message it receives, an actor can: make local decisions, create ...

. But the largest influence that MDL had was on the

software Software consists of computer programs that instruct the Execution (computing), execution of a computer. Software also includes design documents and specifications. The history of software is closely tied to the development of digital comput ...

genre of

interactive fiction Interactive fiction (IF) is software simulating environments in which players use text Command (computing), commands to control Player character, characters and influence the environment. Works in this form can be understood as literary narrati ...

(IF). An IF game named

Zork ''Zork'' is a text adventure game first released in 1977 by developers Tim Anderson (programmer), Tim Anderson, Marc Blank, Bruce Daniels, and Dave Lebling for the PDP-10 mainframe computer. The original developers and others, as the company ...

, sometimes called Dungeon, was first written in MDL. Later, Reeve, Daniels, Galley and other members of Dynamic Modeling went on to start

Infocom Infocom, Inc., was an American software company based in Cambridge, Massachusetts, that produced numerous works of interactive fiction. They also produced a business application, a relational database called ''Cornerstone (software), Cornerston ...

, 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

to create their award winning games.

Code sample

This is a sample of PDP-10 MDL: EST ROOM) ) ) ( > ) ( .RMS>> ) ( .RMS> .RMS>>> )>> .EXITS>>

References

External links

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

Code sample

See also

References

External links