Coordinates	32°30′20″N45°49′29″N
name	BCPL
paradigm	procedural, imperative, structured
year	1966
designer	Martin Richards
typing	typeless
influenced by	CPL
influenced	B (indirectly C)
website	}}

BCPL (Basic Combined Programming Language) is a procedural, imperative, and structured computer programming language designed by Martin Richards of the University of Cambridge in 1966.

Design

Originally intended for writing compilers for other languages, BCPL is no longer in common use. However, its influence is still felt because a stripped down and syntactically changed version of BCPL, called B, was the language on which the C programming language was based. This important fact led many C programmers to humorously issue the backronym Before C Programming Language. BCPL was the first brace programming language, and the braces survived the syntactical changes and have become a common means of denoting program source code statements. In practice, on limited keyboards of the day, source programs often used the sequences $( and $) in place of the symbols { and }. The single-line '//' comments of BCPL, which were not taken up in C, reappeared in C++, and later in C99.

BCPL was a response to difficulties with its predecessor Combined Programming Language (CPL), created during the early 1960s. Richards created BCPL by "removing those features of the full language which make compilation difficult". The first compiler implementation, for the IBM 7094 under Compatible Time-Sharing System (CTSS), was written while Richards was visiting Project MAC at the Massachusetts Institute of Technology (MIT) in the spring of 1967. The language was first described in a paper presented to the 1969 Spring Joint Computer Conference.

The language is clean, consistent, powerful, and portable. It thus proved possible to write small and simple compilers for it; reputedly some compilers could be run in 16 kilobytes. Further, the Richards compiler, itself written in BCPL, was easily portable. BCPL was thus a popular choice for bootstrapping a system.

A major reason for the compiler's portability lay in its structure. It was split into two parts: the front end parsed the source and generated O-code for a virtual machine, and the back end took the O-code and translated it into the code for the target machine. Only 1/5 of the compiler's code needed to be rewritten to support a new machine, a task that usually took between 2 and 5 man-months. This approach became common practice later, e.g., Pascal or Java, but the Richards BCPL compiler was the first to define a virtual machine for this purpose.

The language is unusual in having only one data type: a word, a fixed number of bits, usually chosen to align with the architecture's machine word and of adequate capacity to represent any valid storage address. For many machines of the time, this data type was a 16-bit word. This choice later proved to be a significant problem when BCPL was used on machines in which the smallest addressable item was not a word, but a byte or on machines with larger word sizes: 32-bit and 64-bit words, which allowed them to manage large address spaces.

The interpretation of any value was determined by the operators used to process the values. (For example, + added two values together treating them as integers; ! indirected through a value, effectively treating it as a pointer.) In order for this to work, the implementation provided no type checking. The Hungarian notation was developed to help programmers avoid inadvertent type errors.

The mismatch between BCPL's word orientation and byte-oriented hardware was addressed in several ways. One was providing standard library routines for packing and unpacking words into byte strings. Later, two language features were added: the bit-field selection operator and the infix byte indirection operator (denoted by the '%' character).

BCPL handles bindings spanning separate compilation units in a unique way. There are no user-declarable global variables; instead there is a global vector, which is similar to "blank common" in Fortran. All data shared between different compilation units comprises scalars and pointers to vectors stored in a pre-arranged place in the global vector. Thus the header files (files included during compilation using the "GET" directive) become the primary means of synchronizing global data between compilation units, containing "GLOBAL" directives that present lists of symbolic names, each paired with a number that associates the name with the corresponding numerically addressed word in the global vector. As well as variables, the global vector also contains bindings for external procedures. This makes dynamic loading of compilation units very simple to achieve. Instead of relying on the link loader of the underlying implementation, effectively BCPL gives the programmer control of the linking process.

The global vector also made it very simple to replace or augment standard library routines. A program could save the pointer from the global vector to the original routine and replace it with a pointer to an alternative version. The alternative might call the original as part of its processing. This could be used as a quick ad-hoc debugging aid.

BCPL is reputedly the language in which the original hello world program was written. The first MUD was also written in BCPL.

Several operating systems were written partially or wholly in BCPL (for example, TRIPOS and significant parts of AmigaOS, including Kickstart and the earliest versions of AmigaDOS). BCPL was also the initial language used in the seminal Xerox PARC Alto project, the first modern personal computer; among other projects, the Bravo document preparation system was written in BCPL.

By 1970, implementations existed for the Honeywell 635 and Honeywell 645, the IBM 360, the TX-2, the CDC 6400, the UNIVAC 1108, the PDP-9, the KDF 9 and the Atlas 2. There was also a version produced for the BBC Micro in the mid 1980s by Richards Computer Products, a company started by John Richards, the brother of Dr. Martin Richards. The BBC Domesday Project made use of the language. Versions of BCPL for the Amstrad CPC and Amstrad PCW computers were also released in 1986 by UK software house Arnor Ltd.

In 1979 implementations of BCPL existed for at least 25 architectures; in 2001 it sees little use.

The philosophy of BCPL can be summarised by quoting from the book ''BCPL, the language and its compiler'':

The design, and philosophy, of BCPL strongly influenced B, which in turn influenced C.

There are rumours that BCPL actually stood for "Bootstrap Cambridge Programming Language", however CPL was never created since development stopped at BCPL, and the acronym was reinterpreted for the BCPL book.

Examples

These complete and compilable examples are from Martin Richards' BCPL distribution.

Printing factorials:

GET "libhdr"



LET start() = VALOF
{ FOR i = 1 TO 5 DO writef("fact(%n) = %i4*n", i, fact(i))
  RESULTIS 0
}



AND fact(n) = n=0 -> 1, n*fact(n-1)

Counting solutions to the N queens problem:

GET "libhdr"


GLOBAL { count:200; all:201  }


LET try(ld, row, rd) BE TEST row=all



THEN count := count + 1



ELSE { LET poss = all & ~(ld | row | rd)
                               UNTIL poss=0 DO
                               { LET p = poss & -poss
                                 poss := poss - p
                                 try(ld+p << 1, row+p, rd+p >> 1)
                               }
                             }



LET start() = VALOF
{ all := 1


  FOR i = 1 TO 12 DO
  { count := 0
    try(0, 0, 0)
    writef("Number of solutions to %i2-queens is %i5*n", i, count)
    all := 2*all + 1
  }


RESULTIS 0
}

References

Martin Richards, ''[http://www.fh-jena.de/~kleine/history/languages/Richards-BCPL-ReferenceManual.pdf The BCPL Reference Manual]'' (Memorandum M-352, Project MAC, Cambridge, July, 1967)

Martin Richards, ''BCPL - a tool for compiler writing and systems programming'' (Proceedings of the Spring Joint Computer Conference, Vol 34, pp 557–566, 1969)

Martin Richards, Arthur Evans, Robert F. Mabee, ''The BCPL Reference Manual'' (MAC TR-141, Project MAC, Cambridge, 1974)

Martin Richards, C. Whitby-Strevens, ''BCPL, the language and its compiler'' (Cambridge University Press, 1980) ISBN 0-521-28681-6

External links

Martin Richards' BCPL distribution

[http://63.249.85.132/langs/bcpl/bcpl.html Martin Richards's BCPL Reference Manual] by Dennis M. Ritchie also includes some fascinating commentary from him about BCPL's influence on C

BCPL entry in the Jargon File

Nordier & Associates' x86 port

ArnorBCPL manual

Category:Procedural programming languages Category:Structured programming languages Category:Systems programming languages Category:Programming languages created in 1966 Category:University of Cambridge Computer Laboratory

ar:لغة البرمجة الأساسية المختلطة bn:বিসিপিএল ca:BCPL da:BCPL de:Basic Combined Programming Language es:BCPL fa:بی‌سی‌پی‌ال fi:BCPL fr:BCPL gl:BCPL id:BCPL it:BCPL ja:BCPL nl:BCPL pl:BCPL pt:BCPL ru:BCPL zh:BCPL

Northern Kentucky is the name often given to the northernmost (most typically the three northernmost) counties in Kentucky (Boone, Kenton, Campbell, shown in red on the map). Gallatin, Grant, Pendleton, and Bracken counties (highlighted in pink on the map) are often group with the aforementioned and are officially part of the Cincinnati Metropolitan Area, and are sometimes included in definitions of "Northern Kentucky". Historically, Trimble and Mason counties have also been included in "Northern Kentucky".

The three northernmost counties of Kentucky each has at least one major center of population: Florence in Boone County; Covington, Erlanger, and Independence in Kenton County; and Newport, Fort Thomas, and Alexandria in Campbell County. Immediately on the northern side of the Ohio River from Covington and Newport is Cincinnati, Ohio. However, the entire core region is relatively densely populated, with these cities surrounded by many smaller towns which have little other than a city limit sign between them. The periphery of Boone, Kenton, and Campbell Counties, namely the western half of Boone County, and southernmost parts of all three of the core counties, are still primarily rural in nature. The four outer counties are still primarily rural. Combined with the southeast corner of Indiana, and Southwestern Ohio, all seven counties are a part of the Greater Cincinnati area, which has a population over two million.

The area was served by ferry service across the Ohio River until the completion of the John A. Roebling Suspension Bridge (prototype of the famous Brooklyn Bridge) in 1866, whereupon land values in the areas near the river quadrupled overnight.

Beginning in the 1970s, many factors combined to create major growth. The proximity to Cincinnati, the completion of I-75, the nexus of rail service and river traffic, creation of several industrial parks, and the growth of Cincinnati/Northern Kentucky International Airport (located near Hebron in northeastern Boone County near the Kenton County line) drew many industries into the area. Its geographically central location (within 800 miles of 80% of the US population) makes it ideal for distribution centers, and those shipping all over the country.

Climate

Northern Kentucky is located within a climatic transition zone and is at the extreme northern limit of the humid subtropical climate. Evidence of both humid subtropical climate and humid continental climate can be found here, particularly noticeable by the presence of plants indicative of each climatic region; for example, the Southern magnolia, Crape-myrtle, and Needle palm from the subtropics and the Blue spruce, Maple, and Eastern Hemlock from cooler regions are successful landscape plants in and around Northern Kentucky. Some significant moderating variables for the overall climate of Northern Kentucky include: the Ohio River, the region's relatively large hills and valleys, and an urban heat influence due to the proximity of the Cincinnati/Northern Kentucky metropolitan area. The wall lizard, introduced from Italy in the 1950s, is an example of fauna in the area that lends a subtropical ambiance to the region. Northern Kentucky is considered to be within the periphery of both the Midwest and the Upland South.

{|style="width:99%" frame="box" rules="all" cellpadding="1" |-style="background-color:#CCFFFF;text-align:center;" !Geographic Area !July 1, 2008 !July 1, 2005 !Census 2000 !1990 Census !1980 Census !1970 Census !1960 Census !1950 Census |- |TOTAL |417,079 |403,336 |362,741 |315,390 |302,583 |282,257 |261,191 |225,353 |- |Boone County, Kentucky |115,231 |106,272 |85,991 |57,589 |45,842 |32,812 |style="background-color:#FFFFAA"|21,940¹ |style="background-color:#FFFFAA"|13,015¹ |- |Bracken County, Kentucky |style="background-color:#FFFFAA"|8,569 |style="background-color:#FFFFAA"|8,279¹ |style="background-color:#FFFFAA"|7,766¹ |style="background-color:#FFFFAA"|7,738¹ |style="background-color:#FFFFAA"|7,227¹ |style="background-color:#FFFFAA"|7,422¹ |style="background-color:#FFFFAA"|8,424¹ |- |Campbell County, Kentucky |87,038 |87,251 |88,616 |83,866 |83,317 |88,501 |86,803 |76,196 |- |Gallatin County, Kentucky |8,071 |8,134 |7,870 |style="background-color:#FFFFAA"|5,393¹ |style="background-color:#FFFFAA"|4,842¹ |style="background-color:#FFFFAA"|4,134¹ |style="background-color:#FFFFAA"|3,867¹ |style="background-color:#FFFFAA"|3,969¹ |- |Grant County, Kentucky |25,549 |24,610 |22,384 |style="background-color:#FFFFAA"|15,737¹ |style="background-color:#FFFFAA"|13,308¹ |style="background-color:#FFFFAA"|9,999¹ |style="background-color:#FFFFAA"|9,489¹ |style="background-color:#FFFFAA"|9,809¹ |- |Kenton County, Kentucky |157,629 |153,665 |151,464 |142,031 |137,058 |129,440 |120,700 |104,254 |- |Pendleton County, Kentucky |14,992 |15,125 |14,390 |style="background-color:#FFFFAA"|12,036¹ |style="background-color:#FFFFAA"|10,989¹ |style="background-color:#FFFFAA"|9,949¹ |style="background-color:#FFFFAA"|9,968¹ |style="background-color:#FFFFAA"|9,610¹ |- |}

External links

Historical Northern Kentucky Images and Texts

Northern Kentucky Convention and Visitors Bureau

Northern Kentucky Forums

Boone County Arboretum

Category:Boone County, Kentucky Category:Campbell County, Kentucky Category:Geography of Greater Cincinnati Category:Kenton County, Kentucky Category:Regions of Kentucky