POP-2, often referred to as POP2 was a programming language developed around 1970 from the earlier language POP-1 (originally named COWSEL) by Robin Popplestone and Rod Burstall at the University of Edinburgh. A programming language is an Artificial language that can be used to write programs which control the behavior of a machine particularly a Computer. COWSEL ( COntrolled Working SpacE Language) is a Programming language designed between 1964 and 1966 by Robin Popplestone. Robin John Popplestone ( 9 December 1938 - 14 April 2004) was a pioneer in the fields of Machine intelligence and Robotics Roderick Burstall was one of three founders of the Edinburgh Laboratory for Foundations of Computer Science. The University of Edinburgh (Oilthigh Dhùn Èideann founded in 1582 is a renowned centre for teaching and research in Edinburgh, Scotland, UK. It drew roots from many sources: the languages LISP and ALGOL 60, and theoretical ideas from Landin. Lisp (or LISP) is a family of Computer Programming languages with a long history and a distinctive fully parenthesized syntax Algol (β Per / Beta Persei known colloquially as the Demon Star, is a bright Star in the Constellation Perseus. Peter Landin is a British Computer scientist. He was one of the first to realize that the Lambda calculus could be used to model a programming language It used an incremental compiler, which gave it some of the flexibility of an interpreted language, including allowing new function definitions at run time and modification of function definitions while a program was running (both of which are features of dynamic compilation), without the overhead of an interpreted language. Generally a Compiler for a Programming language is a piece of software that reads in one or more program files in a source language and outputs one or more files containing In Computer programming an interpreted language is a Programming language whose implementation often takes the form of an interpreter. Dynamic compilation is a process used by some programming language implementations to gain performance during program execution It has been described as 'The first true functional language' at HOPL, the History of Programming Languages web site.
Its syntax was Algol-like, except that assignments were backwards: instead of writing
a := 3;
one wrote
3 -> a;
The reason for this was that the language had explicit notion of an operand stack; thus, the previous assignment could be written as two separate statements:
3;
which evaluated the value 3 and left it on the stack, and
-> a;
which popped the top value off the stack and assigned it to the variable 'a'. In Computer science, a stack is an Abstract data type and Data structure based on the principle of Last In First Out (LIFO Similarly, the function call
f(x, y, z);
could be written as
x, y, z; f();
(commas and semicolons being largely interchangeable) or even
x, y, z. f;
or
(x, y, z). f;
There were no special language constructs for creating arrays or record structures as they are commonly understood: instead, these were created with the aid of special builtin functions, e. g. newarray (for arrays that could contain any type of item) and newanyarray for creating restricted types of items.
Thus, array element and record field accessors were simply special cases of a doublet function: this was a function that had another function attached as its updater, which was called on the receiving side of an assignment. Thus, if the variable a contained an array, then
3 -> a(4);
was equivalent to
updater(a)(3, 4);
the builtin function updater returning the updater of the doublet. Of course, updater was itself a doublet and could be used to change the updater component of a doublet.
Because of the stack-based paradigm, there was no need to distinguish between statements and expressions; thus, the two constructs
if a > b then
c -> e
else
d -> e
close;
and
if a > b then
c
else
d
close -> e;
were equivalent (note the use of close as endif hadn't been invented yet).
Variables could hold values of any type, including functions, which were first-class objects. Thus, the following constructs
function max x y; if x > y then x else y close end;
and
vars max; lambda x y; if x > y then x else y close end -> max;
were equivalent.
An interesting operation on functions was partial application; this was where some number of the rightmost arguments of the function were frozen to given values, to produce a new function of fewer arguments. For instance, consider a function for computing general second-degree polynomials:
function poly2 x a b c; a * x * x + b * x + c end;
This could be bound, for instance as
vars less1squared; poly2(% 1, -2, 1 %) -> less1squared;
such that the expression
less1squared(3)
returns the square of (3 - 1), which is 4.
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Later Developments
The original version of POP-2 was implemented on an Elliott 4130 computer in the University of Edinburgh (with only 64KB RAM, doubled to 128KB in 1972).
At middle 1970s POP-2 was ported on BESM-6 (POPLAN System). Year 1970 ( MCMLXX) was a Common year starting on Thursday (link shows full calendar of the Gregorian calendar. This article is about the Soviet computer "BESM" redirects here
Later versions were implemented for Modula One, PDP-10, ICL 1900 series (running the George operating system). The PDP-10 was a Mainframe computer manufactured by Digital Equipment Corporation (DEC from the late 1960s on the name stands for "Programmed Data Processor ICT 1900 is the name given to a series of Mainframe computers released by International Computers and Tabulators (ICT in the 1960s Julian Davies, in Edinburgh, implemented an extended version of POP-2, which he called POP-10 on the PDP-10 computer running TOPS-10. The TOPS-10 System was a computer Operating system from Digital Equipment Corporation (DEC for the PDP-10 released in 1964, the resulting systems This was the first dialect of POP-2 that treated case as significant in identifier names, used lower case for most system identifiers, and supported long identifiers with more than 8 characters.
Shortly after that, a new implementation known as WPOP (for WonderPop) was implemented by Robert Rae and Allan Ramsay in Edinburgh, on a research-council funded project. That version introduced caged address spaces, some compile-time syntactic typing (e. g. for integers and reals) as well as some pattern matching constructs for use with a variety of data-structures.
In parallel with that Steve Hardy at Sussex University implemented a subset of POP-2, which he called POP-11 which ran on a DEC PDP-11/40 computer. POP-11 is a powerful reflective, incrementally compiled Programming language with many of the features of an Interpreted language. It was originally designed to run on the DEC operating system RSX-11D, in time-shared mode for teaching, but that caused so many problems that an early version of Unix was installed and used instead. Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer That version was written in Unix assembler, and code was incrementally compiled to an intermediate byte code which was interpreted. That port was completed around 1976 and as a result Pop-11 was used in several places for teaching. In order to support its teaching function many of the syntactic features of POP-2 were modified, e. g. replacing function . . . end with define . . . enddefine and adding a wider variety of looping constructs with closing brackets to match their opening brackets instead of the use of close for all loops in POP-2. Pop-11 also introduced a pattern matcher for list structures, making it much easier to teach AI programming.
Around 1980 Pop-11 was ported to a VAX-780 computer by Steve Hardy and John Gibson, and soon after that it was replaced by a full incremental compiler (producing machine-code instead of an interpreted intermediate code). The existence of the compiler and all its subroutines at run time made it possible to support far richer language extensions than were possible with Macros, and as a result Pop-11 was used (by Steve Hardy, Chris Mellish and John Gibson)) to produce an implementation of Prolog, using the standard syntax of Prolog, and the combined system became known as Poplog, to which Common Lisp and Standard ML were later added. Prolog is a Logic programming language It is a general purpose language often associated with Artificial intelligence and Computational linguistics Poplog is a powerful multi- language, multiparadigm, reflective, incrementally compiled software development environment Common Lisp, commonly abbreviated CL, is a dialect of the Lisp Programming language, published in ANSI standard document Information Standard ML ( SML) is a general-purpose modular, Functional programming language with Compile-time type checking and Type inference This version was later ported to a variety of machines and operating systems and as a result Pop-11 became the dominant dialect of POP-2, still available in the Poplog system.
Around 1986 a new AI company Cognitive Applications Ltd. , collaborated with members of Sussex university to produce a variant of Pop-11 called AlphaPop running on Apple Mac computers, with integrated graphics. This was used for a number of commercial projects, as well as being used for teaching AI programming in several universities. The fact that it was implemented in an early dialect of C, using an idiosyncratic compiler made it very hard to maintain and upgrade to new versions of the Mac operating system. In addition to this, AlphaPop was not "32-bit clean" due to the use of high address bits as "tag bits" to signify the type of objects, which was incompatible with the use of memory above 8Mb on later Macintoshes.
See also
- COWSEL programming language
- POP-1 programming language
- POP-11 programming language
- Poplog programming environment
External links
References
R. COWSEL ( COntrolled Working SpacE Language) is a Programming language designed between 1964 and 1966 by Robin Popplestone. COWSEL ( COntrolled Working SpacE Language) is a Programming language designed between 1964 and 1966 by Robin Popplestone. POP-11 is a powerful reflective, incrementally compiled Programming language with many of the features of an Interpreted language. Poplog is a powerful multi- language, multiparadigm, reflective, incrementally compiled software development environment Burstall, J. Collins and R. Popplestone Programming in Pop-2 University Press, Edinburgh, 1968
D. J. M. Davies, POP-10 Users' Manual, Computer Science Report #25, University of Western Ontario, 1976
R. Smith, A. Sloman and J. Gibson, POPLOG's two-level virtual machine support for interactive languages, in Research Directions in Cognitive Science Volume 5: Artificial Intelligence, Eds. D. Sleeman and N. Bernsen, Lawrence Erlbaum Associates, pp. 203--231, 1992.
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