ALGOL 58

ALGOL 58

Paradigm	procedural,imperative,structured
Family	ALGOL
Designed by	Friedrich L. Bauer,Hermann Bottenbruch,Heinz Rutishauser,Klaus Samelson,John Backus,Charles Katz,Alan Perlis,Joseph Henry Wegstein
First appeared	1958(1958)
Typing discipline	Static,strong
Scope	Lexical
Influenced by
FORTRAN,IT,Plankalkül,Superplan,Sequentielle Formelübersetzung
Influenced
Most subsequent imperative languages (Algol-like)

ALGOL 58,originally namedIAL,is one of the family ofALGOLcomputerprogramming languages.It was an early compromise design soon superseded byALGOL 60.According toJohn Backus: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...

ALGOL 58 introduced the fundamental notion of thecompound statement,but it was restricted tocontrol flowonly, and it was not tied toidentifier scopein the way that Algol 60'sblockswere.

Name

Bauer attributes the name toHermann Bottenbruch,who coined the termalgorithmic language(algorithmische Sprache) in 1957, "at least in Germany".

History

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 Zurichand was attended by the following people:

• Friedrich L. Bauer,Hermann Bottenbruch,Heinz Rutishauser,andKlaus Samelson(from the GAMM)
• John Backus,Charles Katz,Alan Perlis,andJoseph Henry Wegstein(from the ACM).

The language was originally proposed to be calledIAL(International Algebraic Language) but according to Perlis, 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.

By the end of 1958 the ZMMD-group had built a working ALGOL 58 compiler for theZ22computer. 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 Collegeon anLGP-30,but that implementation soon evolved intoALGOL 60.An implementation for theBurroughs220 calledBALGOLevolved along its own lines as well, but retained much of ALGOL 58's original character.

ALGOL 58's primary contribution was to later languages; it was used as a basis forJOVIAL,MAD,NELIACandALGO.It was also used during 1959 to publishalgorithmsinCACM,beginning a trend of using ALGOL notation in publication that continued for many years.

Time line of implementations of ALGOL 58 variants

Name	Year	Author	State	Description	Target CPU
ZMMD-implementation	1958	Friedrich L. Bauer,Heinz Rutishauser, Klaus Samelson, Hermann Bottenbruch	Germany		Z22
NELIAC	1958	Naval Electronics Laboratory	USA		AN/USQ-17
JOVIAL	1960	Jules Schwartz	USA	Was theDODHOLprior toAda (programming language)	Various (see article)
BALGOL	1960	Joel Merner et al.	USA		Burroughs CorporationB220
MAD	1960	University of Michigan	USA		IBM 7090/7094 mainframe, then mid-1960s ported toUnivac 1108
Dartmouth ALGOL 30	1962	Thomas Eugene Kurtzet al. - evolved into ALGOL 60	USA		LGP-30
SUBALGOL	1962	Bob Braden,Lawrence M. BreedandRoger Moore,Stanford University	USA	BALGOL extension	IBM 7090
ALGO	~	Bendix Corporation	USA		Bendix G-15

ALGOL 58's influence on ALGOL 60

• 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.
• 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 statementin C and other languages.
• In-line functions of the formf(x):=x/ 2;were proposed in IAL butdroppedin ALGOL 60.
• IAL procedure declarations provide separate declaration lists for input and output parameters, a procedure can return multiple values; this mechanism wasreplacedin ALGOL 60 with thevaluedeclaration.
• Variable declarations in IAL can be placedanywherein the program and not necessarily at the beginning of a procedure. In contrast, the declarations within an ALGOL 60 block should occurbeforeall 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 keywordFürwith the direct English translationfor;ALGOL 60 replaced the parentheses with the word delimitersstepanduntil,such that the previous statement instead would bei:=basestepincrementuntillimit.
• The IALif-statement does not have athen-clause orelse-clause; it ratherguardsthe succeeding statement. IAL provides anif either-statement that cleanly allows testing of multiple conditions. Both were replaced by ALGOL'sif-thenconstruct, 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.

External links

• Algol 58at the Software Preservation Group (cf.Computer History Museum)
• Algol 58 report from CACMat the Software Preservation Group