ALGOL 58, originally namedIAL, is a member of theALGOL family of computerprogramming languages. It was an early compromise design soon superseded byALGOL 60. According toJohn Backus:
The Zurich ACM-GAMM Conference had two principal motives in proposing the IAL: (a) To provide a means of communicating numerical methods and other procedures between people, and (b) To provide a means of realizing a stated process on a variety of machines...[2]
Bauer attributes the name toHermann Bottenbruch, who coined the termalgorithmic language (algorithmische Sprache) in 1957, "at least in Germany".[3][4]
There were proposals for a universal language by theAssociation for Computing Machinery (ACM) and also by the GermanGesellschaft für Angewandte Mathematik und Mechanik ("Society of Applied Mathematics and Mechanics") (GAMM). It was decided to organize a joint meeting to combine them. The meeting took place from May 27 to June 2, 1958, atETH Zurich and was attended by the following people:
The language was originally proposed to be calledIAL (International Algebraic Language) but according to Perlis,[5]this was rejected as an "'unspeakable' and pompous acronym". ALGOL was suggested instead, though not officially adopted until a year later. The publication following the meeting still used the name IAL.[6]
By the end of 1958 the ZMMD-group had built a working ALGOL 58 compiler for theZ22 computer. ZMMD was an abbreviation for Zürich (where Rutishauser worked), München (workplace of Bauer and Samelson), Mainz (location of the Z22 computer), Darmstadt (workplace of Bottenbruch).
ALGOL 58 saw some implementation effort atIBM, but the effort was in competition withFORTRAN, and soon abandoned. It was also implemented atDartmouth College on anLGP-30, but that implementation soon evolved intoALGOL 60. An implementation for theBurroughs 220 calledBALGOL evolved along its own lines as well, but retained much of ALGOL 58's original character.[7]
ALGOL 58's primary contribution was to later languages; it was used as a basis forJOVIAL,[4]MAD,NELIAC[4] andALGO. It was also used during 1959 to publishalgorithms inCACM, beginning a trend of using ALGOL notation in publication that continued for many years.
IAL introduced the three-level concept of reference, publication and hardware language, and the concept of "word delimiters" having a separate representation from freely chosen identifiers (hence, no reserved words). ALGOL 60 kept this three-level concept.[8]
The distinction between assignment (:= representing a left-facing arrow) and the equality relation= was introduced in IAL and kept in ALGOL 60.
Both IAL and ALGOL 60 allow arrays with arbitrary lower and upper subscript bounds, and allow subscript bounds to be defined by integer expressions.
Both IAL and ALGOL 60 allow nesting of procedure declarations and the corresponding identifier scopes.
The IAL report described parameter substitution in much the same terms as the ALGOL 60 report, leaving open the possibility ofcall by name. It is unclear if this was realized at the time.
IAL allows numeric statement labels, that ALGOL 60 kept.
The possibility of including non-ALGOL code within a program was already hinted at, in the context of parameters to procedures.
Both IAL and ALGOL 60 have aswitch designator, unrelated, however, to theswitch statement in C and other languages.
In-line functions of the formf(x) :=x / 2; were proposed in IAL butdropped in ALGOL 60.
IAL procedure declarations provide separate declaration lists for input and output parameters, a procedure can return multiple values; this mechanism wasreplaced in ALGOL 60 with thevalue declaration.
Variable declarations in IAL can be placedanywhere in the program and not necessarily at the beginning of a procedure. In contrast, the declarations within an ALGOL 60 block should occurbefore all execution statements.
Thefor-statement has the formfor i:=base(increment)limit, directly resembling the loop of Rutishauser's programming languageSuperplan, replacing=with:=, and replacing its German keywordFür with the direct English translationfor; ALGOL 60 replaced the parentheses with the word delimitersstep anduntil, such that the previous statement instead would bei:=basestepincrementuntillimit.
The IALif-statement does not have athen-clause orelse-clause; it ratherguards the succeeding statement. IAL provides anif either-statement that cleanly allows testing of multiple conditions. Both were replaced by ALGOL'sif-then construct, with the introduction of the "dangling-else" ambiguity.
IAL provides macro-substitution with thedo-statement; this was dropped in ALGOL 60.
IAL allows one or more array subscripts to be omitted when passing arrays to procedures, and to provide any or all arguments to a procedure passed to another procedure.
IAL's infix Boolean operators are all of the same precedence level. Exponents are indicated with paired up and down arrows, which removed any confusion about the correct interpretation of nested exponents; ALGOL 60 replaced the paired arrows with a single up-arrow whose function is equivalent to FORTRAN's**.
The IAL report does not explicitly specify which standard functions were to be provided, making a vague reference to the "standard functions of analysis." The ALGOL 60 report has a more explicit list of standard functions.
^Backus, J.W. (1959). "The Syntax and Semantics of the Proposed International Algebraic Language of Zürich ACM-GAMM Conference".Proceedings of the International Conference on Information Processing. UNESCO. pp. 125–132.
^Perlis, A.J. (1981). "Talk on Computing in the fifties".ACM National Conference. Nashville, TN. Los Alamito, CA: (Transcript in J. A. N. Lee (ed.), Computer Pioneers, IEEE Computer Society Press (published 1995). pp. 545–556).
^"Algol 58 implementations and dialects",Software Preservation Group,Computer History Museum.Donald Knuth is quoted on BALGOL: "I’m in my second year at Caltech, and I was a consultant to Burroughs. After finishing my compiler for Burroughs, I joined the Product Planning Department. The Product Planning Department was largely composed of people who had written the best software ever done in the world up to that time, which was a Burroughs ALGOL compiler for the 220 computer. That was a great leap forward for software. It was the first software that used list processing and high level data structures in an intelligent way. They took the ideas of Newell and Simon and applied them to compilers. It ran circles around all the other things that we were doing." [Don Knuth, CHM Oral History, 2007, page 9]
