Editing Plankalkül (section)

==History of programming==
In the domain of creating computing machines, Zuse was self-taught, and developed them without knowledge about other mechanical computing machines that existed already – although later on (building the [[Z3 (computer)|Z3]]) being inspired by [[David Hilbert|Hilbert]]'s and [[Wilhelm Ackermann|Ackermann]]'s book on elementary mathematical logic (see [[Principles of Mathematical Logic]]).<ref name="Hellige_2004"/>{{rp|pages=113, 152, 216}} To describe logical circuits, Zuse invented his own diagram and notation system, which he called "combinatorics of conditionals" ({{langx|de|Bedingungskombinatorik}}). After finishing the [[Z1 (computer)|Z1]] in 1938, Zuse discovered that the calculus he had independently devised already existed and was known as [[propositional calculus]].<ref name="Rojas-Göktekin-Friedland-Krüger-Kuniß-Langmack_2004"/>{{rp|page=3}} What Zuse had in mind, however, needed to be much more powerful (propositional calculus is not [[Turing-complete]] and is not able to describe even simple arithmetic calculations<ref name="Turing_2013"/>). In May 1939, he described his plans for the development of what would become Plankalkül.<ref name="Hellige_2004"/>{{rp|pages=113, 152, 216}} He wrote the following in his notebook:

{{Verse translation|lang=de
|1=Seit etwa einem halben Jahr allmähliches Einführen in die formale Logik. Viele meiner früheren Gedanken habe ich dort wiedergefunden. (Bedingungskombinatorik = Aussagenlogik; Lehre von den Intervallen = Gebietenkalkül). Ich plane jetzt die Aufsetzung des 'Plankalküls'. Hierzu sind eine Reihe von Begriffen zu klären.
|attr2=Konrad Zuse's notebook{{r|name="Rojas-Göktekin-Friedland-Krüger-Kuniß-Langmack_2004"|page=3}}
|2=Almost half a year of gradual introduction into formal logic. I rediscovered there lots of my previous thoughts. (combinatorics of conditionals = [[propositional calculus]]; study of intervals = [[lattice theory]]). I now plan the adoption of "Calculus of plans" onto this. A series of concepts need to be clarified for this.
}}

[[File:"Konrad Zuse-Haus" in Bruck 2.jpg|thumb|right|Historical marker on house in {{ill|Hinterstein|de}} where Zuse worked on Plankalkül]]

While working on his doctoral [[Thesis#Germany|dissertation]], Zuse developed the first known formal system of algorithm notation<ref name="Knuth-Pardo_1976"/>{{rp|page=9}} capable of handling branches and loops.<ref name="Giloi_1997"/>{{rp|page=18}}<ref name="Hellige_2004"/>{{rp|page=56}} In 1942 he began writing a [[computer chess|chess]] program in Plankalkül.<ref name="Hellige_2004"/>{{rp|pages=216-217}} In 1944, Zuse met with the German logician and philosopher [[Heinrich Scholz]], who expressed appreciation for Zuse's utilization of [[logical calculus]].<ref name="Petzold_1992"/> In 1945, Zuse described Plankalkül in an unpublished book.<ref name="Zuse_1945"/> The collapse of [[Nazi Germany]], however, prevented him from submitting his manuscript.<ref name="Giloi_1997"/>{{rp|page=18}}

At that time the only two working computers in the world were [[ENIAC]] and [[Harvard Mark I]], neither of which used a compiler, and ENIAC needed to be reprogrammed for each task by changing how the wires were connected.<ref name="Rojas-Göktekin-Friedland-Krüger-Kuniß-Langmack_2004"/>{{rp|page=3}}

Although most of his computers were destroyed by Allied bombs, Zuse was able to rescue one machine, the [[Z4 (computer)|Z4]], and move it to the Alpine village of [[Hinterstein]]<ref name="Knuth-Pardo_1976"/>{{rp|page=8}} (part of [[Bad Hindelang]]).

{{Cquote
|quote=The very first attempt to devise an algorithmic language was undertaken in 1948 by K. Zuse. His notation was quite general, but the proposal never attained the consideration it deserved.
|author=[[Heinz Rutishauser]], creator of [[ALGOL]]}}

Unable to continue building computers – which was also forbidden by the Allied Powers<ref name="Coy_2004"/> – Zuse devoted his time to the development of a higher-level programming model and language.<ref name="Giloi_1997"/>{{rp|page=18}} In 1948, he published a paper in the ''[[Archiv der Mathematik]]'' and presented at the Annual Meeting of the [[GAMM]].<ref name="Hellige_2004"/>{{rp|page=89}} His work failed to attract much attention.{{Citation needed|date=September 2019}} In a 1957 lecture, Zuse expressed his hope that Plankalkül, "after some time as a [[Sleeping Beauty]], will yet come to life."<ref name="Rojas-Göktekin-Friedland-Krüger-Kuniß-Langmack_2004"/>{{rp|page=3}} He expressed disappointment that the designers of [[ALGOL 58]] never acknowledged the influence of Plankalkül on their own work.<ref name="Giloi_1997"/>{{rp|page=18}}<ref name="Knuth-Pardo_1976"/>{{rp|page=15}}

Plankalkül was republished with commentary in 1972.<ref name="Zuse_1972"/> The first compiler for Plankalkül was implemented by Joachim Hohmann in his 1975 dissertation.<ref name="Hohmann_1979"/> Other independent implementations followed in 1998<ref name="Mauerer_2016"/> and 2000 at the [[Free University of Berlin]].<ref name="Rojas-Göktekin-Friedland-Krüger-Kuniß-Langmack_2004"/>{{rp|page=2}}