Information AboutAlgol |
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ALGOL (short for '''ALGO'''rithmic '''L'''anguage) is a family of Imperative Computer Programming Language s originally developed in the mid 1950s which became the ''de facto'' standard way to report Algorithms in print for almost the next 30 years. It was designed to avoid some of the perceived problems with FORTRAN and eventually gave rise to many other programming languages (including Pascal ). ALGOL uses bracketed statement blocks and was the first language to use '''begin''' '''end''' pairs for delimiting them. Fragments of ALGOL-like syntax are sometimes still used as a notation for algorithms, so-called Pidgin Algol . There are three official main branches of ALGOL family:
Niklaus Wirth based his own Algol-W on ALGOL 60, before moving to develop Pascal. Algol-W was intended to be the next generation ALGOL, but the ALGOL 68 committee decided on a design that was more complex and advanced rather than a cleaned, simplified ALGOL 60. The official ALGOL versions are named after the year they were first published. ''Note: '' Throughout its effective life, the name of the programming language ALGOL was always presented in all-uppercase letters, and this is the practice adopted here. HISTORY ALGOL was developed jointly by a committee of European and American computer scientists in a meeting in 1958 at ETH Zurich . It specified three different syntaxes: a reference syntax, a publication syntax, and an implementation syntax. The different syntaxes permitted it to use different keyword names and conventions for decimal points (commas vs. periods) for different languages. ALGOL was used mostly by research computer scientists in the United States and in Europe. Its use in commercial applications was hindered by the absence of standard input/output facilities in its description and the lack of interest in the language by large computer vendors. ALGOL 60 did however become the standard for the publication of algorithms and had a profound effect on future language development. John Backus developed the Backus Normal Form method of describing programming languages specifically for ALGOL 58. It was revised and expanded by Peter Naur for ALGOL 60, and at the suggestion by Donald Knuth Knuth, Donald E. (1964) Backus Normal Form vs. Backus Naur Form. Communications of the ACM 7(12):735-736 renamed to Backus-Naur Form . Peter Naur: "As editor of the ALGOL Bulletin I was drawn into the international discussions of the language, and was selected to be member of the European language design group in November 1959. In this capacity I was the editor of the ALGOL 60 report, produced as the result of the ALGOL 60 meeting in Paris in January 1960." The following people attended the meeting in Paris (from January 1 to 16):
Alan Perlis gave a vivid description of the meeting: “The meetings were exhausting, interminable, and exhilarating. One became aggravated when one’s good ideas were discarded along with the bad ones of others. Nevertheless, diligence persisted during the entire period. The chemistry of the 13 was excellent.” Both John Backus and Peter Naur served on the committee which created ALGOL 60, as did Wally Feurzeig who later created Logo . ALGOL 60 inspired many languages that followed it; , also involved in implementing the first ALGOL 60 Compiler .). True ALGOL 60s specification and implementation timeline There were about 70 augmented, extensions, derivations and sublanguages of Algol 60 {Link without Title} The Burroughs Large Systems are Stack Machine s designed to be programmed in an extended variant of ALGOL 60, known as Elliott ALGOL ; indeed their Operating System the MCP , was written in Elliott ALGOL as far back as 1961. The Unisys Corporation still markets machines in this family today, running the MCP and supporting a diverse set of Elliott ALGOL compilers. PROPERTIES ALGOL 60 as officially defined had no I/O facilities; implementations defined their own in ways that were rarely compatible with each other. In contrast, ALGOL 68 offered an extensive library of ''transput'' (ALGOL 68 parlance for Input/Output) facilities. ALGOL 60 allowed for two s” that are used to implement it. Donald Knuth devised the “ Man Or Boy Test ” to separate compilers that correctly implemented "recursion and non-local references". This test contains an example of call-by-name. ALGOL 68 was defined using a two-level grammar formalism invented by Adriaan Van Wijngaarden and which bears his name. Van Wijngaarden Grammar s use a Context-free Grammar to generate an infinite set of productions that will recognize a particular ALGOL 68 program; notably, they are able to express the kind of requirements that in many other programming language standards are labelled “semantics” and have to be expressed in ambiguity-prone natural language prose, and then implemented in compilers as ''ad hoc'' code attached to the formal language parser. CODE SAMPLE (ALGOL 60) (The way the bolded text has to be written depends on the implementation, e.g. 'INTEGER' (including the quotation marks) for integer.) procedure Absmax(a) Size:(n, m) Result:(y) Subscripts:(i, k); value n, m; '''array''' a; '''integer''' n, m, i, k; '''real''' y; comment The absolute greatest element of the matrix a, of size n by m is transferred to y, and the subscripts of this element to i and k; begin '''integer''' p, q; y := 0; i := k := 1; for p:=1 '''step''' 1 '''until''' n '''do''' for q:=1 '''step''' 1 '''until''' m '''do''' if abs(a q ) > y '''then''' begin y := abs(a q ); i := p; k := q end end Absmax Here’s an example of how to produce a table using Elliott 803 ALGOL “803 ALGOL” The manual for Elliott 803 ALGOL. . FLOATING POINT ALGOL TEST' BEGIN REAL A,B,C,D' READ D' FOR A:= 0.0 STEP D UNTIL 6.3 DO BEGIN PRINT PUNCH(3),££L??' B := SIN(A)' C := COS(A)' PRINT PUNCH(3),SAMELINE,ALIGNED(1,6),A,B,C' END' END' PUNCH(3) sends output to the teleprinter rather than the tape punch. SAMELINE suppresses the carriage return + line feed normally printed between arguments. ALIGNED(1,6) controls the format of the output with 1 digit before and 6 after the decimal point. TIMELINE: HELLO WORLD The variations and lack of portability of the programs from one implementation to another is easily demonstrated by the classic Hello World Program . ALGOL 58 (IAL) ALGOL 58 had no I/O facilities ALGOL 60 family Since ALGOL 60 had no I/O facilities, there is no portable “Hello World” Program in ALGOL. The following program could (and still will) compile and run on an ALGOL implementation for a Unisys A-Series mainframe, and is a straightforward simplification of code taken from this site . BEGIN FILE F(KIND=REMOTE); EBCDIC ARRAY E {Link without Title} ; REPLACE E BY "HELLO WORLD!";
END. An alternative example, using Elliott Algol I/O is as follows. Elliott Algol used different characters for ‘open-string-quote’ and ‘close-string-quote’, represented here by ‘ and ’. program HiFolks; begin print ‘Hello world’; end; Here’s a version for the Elliott 803 Algol (A104) The standard Elliott 803 used 5 hole paper tape and thus only had upper case. The code lacked any quote characters so £ (UK Pound Sign) was used for open quote and ? (Question Mark) for close quote. Special sequences were placed in double quotes (e.g. ££L?? produced a new line on the teleprinter). HIFOLKS’ BEGIN PRINT £HELLO WORLD££L??’ END’ The ICL 1900 Algol I/O version allowed input from paper tape or punched card. Paper tape 'full' mode allowed lower case. Output was to a line printer. 'BEGIN' 'WRITE TEXT'("HELLO WORLD"); 'END' ALGOL 68 See Also: Algol 68 In the language of the "Algol 68 Report", Input/output facilities were collectively called the " Transput ". ALGOL 68 code was published reserved words were typically lowercase, but bolded or underlined. begin print(("Hello, world!",newline)) end OR using a specific transput channel: begin putf((stand out,$,"Hello, world!")) end For ease of programming on the 7-bit computers of the time there were "official" methods to "BOLD" reserved words, for example, by using uppercase: BEGIN print(("Hello, world!",newline)) END Programmers were sometimes required to totally "THINK IN UPPERCASE" on computers that only had 6-bit characters, eg the " Super Computers ". In this case the above code would be written: 'BEGIN' PRINT(("HELLO, WORLD!",NEWLINE)) 'END' The "Algol 68 Report" was translated into Russian, German, French and Bulgarian, and allowed programming in languages with larger character sets, eg Cyrillic Alphabet . eg the Russian BESM-4 . BEGIN print(("Здравствуй, мир!",newline)) END Note: The 1964 Russian standard GOST 10859 allowed the encoding of 4-bit, 5-bit, 6-bit and 7-bit characters in ALGOL 3. ALGOL 60 RESERVED WORDS AND RESTRICTED IDENTIFIERS There are 35 such reserved words in the standard Burroughs Large Systems sub-language: ALPHA, ARRAY, BEGIN, BOOLEAN, COMMENT, CONTINUE, DIRECT, DO, DOUBLE, ELSE, END, EVENT, FALSE, FILE, FOR, FORMAT, GO, IF, INTEGER, LABEL, LIST, LONG, OWN, POINTER, PROCEDURE, REAL, STEP, SWITCH, TASK, THEN, TRUE, UNTIL, VALUE, WHILE, ZIP.There are 71 such restricted identifiers in the standard Burroughs Large Systems sub-language: ACCEPT, AND, ATTACH, BY, CALL, CASE, CAUSE, CLOSE, DEALLOCATE, DEFINE, DETACH, DISABLE, DISPLAY, DIV, DUMP, ENABLE, EQL, EQV, EXCHANGE, EXTERNAL, FILL, FORWARD, GEQ, GTR, IMP, IN, INTERRUPT, IS, LB, LEQ, LIBERATE, LINE, LOCK, LSS, MERGE, MOD, MONITOR, MUX, NEQ, NO, NOT, ON, OPEN, OR, OUT, PICTURE, PROCESS, PROCURE, PROGRAMDUMP, RB, READ, RELEASE, REPLACE, RESET, RESIZE, REWIND, RUN, SCAN, SEEK, SET, SKIP, SORT, SPACE, SWAP, THRU, TIMES, TO, WAIT, WHEN, WITH, WRITE and also the names of all the intrinsic functions.SEE ALSO NOTES REFERENCES
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