Tony Hoare has died
https://blog.computationalcomplexity.org/2026/03/tony-hoare-1934-2026.htmlI think about this a lot because it’s true of any complex system or argument, not just software.
> The first method is far more difficult. It demands the same skill, devotion, insight, and even inspiration as the discovery of the simple physical laws which underlie the complex phenomena of nature. It also requires a willingness to accept objectives which are limited by physical, logical, and technological constraints, and to accept a compromise when conflicting objectives cannot be met. No committee will ever do this until it is too late.
(All from his Turing Award lecture, "The Emperor's Old Clothes": https://www.labouseur.com/projects/codeReckon/papers/The-Emp...)
This explain quite a lot actually!
"Each of my managers explained carefully his own theory of what had gone wrong and all the theories were different. At last, there breezed into my office the most senior manager of all, a general manager of our parent company, Andrew St. Johnston. I was surprised that he had even heard of me.
"You know what went wrong?" he shouted--he always shouted -- "You let your programmers do things which you yourself do not understand." I stared in astonishment. "
The software I like best was not written by "teams"
I prefer small programs written by individuals that generally violate memes like "software is never finished" and "all software has bugs"
(End user perspective, not a developer)
I was brought in to finish building the interchange format. The previous guy was not up to snuff. The architect I worked for was (with love) a sarcastic bastard who eventually abdicated about 2 rings of the circus to me. He basically took some of the high level meetings and tapped in when one of us thought I might strangle someone.
Their initial impression was that I was a prize to be fought over like a child in a divorce. But the guy who gives you your data has you by the balls, if he is smart enough to realize it, so it went my way nine times out of ten. It was a lot of work threading that needle, (I’ve never changed the semantics of a library so hard without changing the syntax), but it worked out for everyone. By the time we were done the way things worked vs the way they each wanted it to work was on the order of twenty lines of code on their end, which I essentially spoonfed them so they didn’t have a lot of standing to complain. And our three teams always delivered within 15% of estimates, which was about half of anyone else’s error bar so we lowly accreted responsibilities.
I ended up as principal on that project (during a hiring/promotional freeze on that title. I felt bad for leaving within a year because someone pulled strings for that, but I stayed until I was sure the house wouldn’t burn down after I left, and I didn’t have to do that). I must have said, “compromise means nobody gets their way.” About twenty times in or between meetings.
A committee forms when there's widespread disagreement on goals or priorities - representing stakeholders who can't agree. The cost is slower decisions and compromise solutions. The benefit is avoiding tyranny of a single vision that ignores real needs.
Tony might be my favorite computer scientist.
https://www.npr.org/sections/13.7/2014/02/03/270680304/this-...
Antoine de Saint-Exupéry
The book is well worth reading.
One of the Rhino's Party policies stands out - are you sure Trump wasn't born a Cannuck and was stolen at birth by racoons and smuggled down south?
"Annexing the United States, which would take its place as the third territory in Canada's backyard (after the Yukon and the Northwest Territories—Nunavut did not yet exist), in order to eliminate foreign control of Canada's natural resources"
One senior professor, who was helping out with this, asked Dijkstra what is to be done with his correspondences. The professor, quite renowned himself, relates a story where Dijsktra tells him from his hospital bed, to keep the ones with "Tony" and throw the rest.
The professor adds with a dry wit, that his own correspondence with Dijsktra were in the pile too.
I guess back then each letter had a cost, in (delivery) time and money, so you better make it count.
My guess is that these correspondences were often interesting to read because they had to be worthwile to send because of the associated cost.
I can't remember what Oxford did to resolve this, but I think they settled on `C.A.R. Hoare Residence`.
[1] https://www.cs.ox.ac.uk/people/jennifer.watson/tonyhoare.htm...
Anyone else, like me, imagining ML models embodied as Androids attending what amounts to a book club? (I can't quite shake the image of them being little CodeBullets with CRT monitors for heads either.)
Sad to think that the TonyHoare process has reached STOP.
RIP.
I repeatedly borrow this quote from his 1980 Turing Award speech, 'The Emperor's Old Clothes'... "At last, there breezed into my office the most senior manager of all, a general manager of our parent company, Andrew St. Johnston. I was surprised that he had even heard of me. "You know what went wrong?" he shouted--he always shouted-- "You let your programmers do things which you yourself do not understand." I stared in astonishment. He was obviously out of touch with present day realities. How could one person ever understand the whole of a modern software product like the Elliott 503 Mark II software system? I realized later that he was absolutely right; he had diagnosed the true cause of the problem and he had planted the seed of its later solution."
My interpretation is that whether shifting from delegation to programmers, or to compilers, or to LLMs, the invariant is that we will always have to understand the consequences of our choices, or suffer the consequences.
It would have been fun if he’d directly said “You’re absolutely right!”
That was 35ish years ago. I just pulled up the paper now and I can't read the notation anymore... This might be something that I try applying an AI to. Get it to walk me through a paper paragraph-by-paragraph until I get back up to speed.
Retrospective: An Axiomatic Basis For Computer Programming. This was written 30 years after An Axiomatic Basis for Computer Programming to take stock on what was proven right and what was proven wrong - https://cacm.acm.org/opinion/retrospective-an-axiomatic-basi...
How Did Software Get So Reliable Without Proof? More detailed paper on the above theme (pdf) - https://6826.csail.mit.edu/2020/papers/noproof.pdf
It is very interesting to see how Sir Tony diverged from EDW: one is right in theoretical sense but cynical about human fallacies and how the society is heading towards more wasteful complexity, one is to live with it and stay optimistic.
There is a proverb in Chinese Taoism:
小隱隱於野，大隱隱於市
A small recluse hides in the wild, while a great recluse hides in the city
Several keywords used in many programming languages come from Hoare, who either coined them himself, or he took them from another source, but all later programming language designers took them from Hoare. For example "case", but here only the keyword comes from Hoare, because a better form of the "case" statement had been proposed first by McCarthy many years earlier, under the name "select".
Another example is "class" which Simula 67, then all object-oriented languages took from Hoare, However, in this case the keyword has not been used first by Hoare, because he took "class", together with "record", from COBOL.
Another keyword popularized by Hoare is "new" (which Hoare took from Wirth, but everybody else took from Hoare), later used by many languages, including C++. At Hoare, the counterpart of "new" was "destroy", hence the name "destructor", used first in C++.
The paper "Record Handling", published by C.A.R. Hoare in 1965-11 was a major influence on many programming languages. It determined significant changes in the IBM PL/I programming language, including the introduction of pointers . It also was the source of many features of the SIMULA 67 and ALGOL 68 languages, from where they spread in many later programming languages.
The programming language "Occam" has been designed mainly as an implementation of the ideas described by Hoare in the "Communicating Sequential Processes" paper published in 1978-08. OpenMP also inherits many of those concepts, and some of them are also in CUDA.
His “billion dollar mistake”:
https://www.infoq.com/presentations/Null-References-The-Bill...
He states around minute 25 the solution to the problem is to explicitly represent null in the type system, so nullable pointers are explicitly declared as such. But it can be complex to ensure that non-nullable references are always initialized to a non-null value, which is why he chose the easy solution to just let every reference be nullable.
Optional types were a very valuable invention and the fact that null values have been handled incorrectly in many programming languages or environments is not Hoare's fault.
there was a time, 10-15 years ago, when they were super cool. at some point they """diluted""" the technicality content and the nature of guests and they vanished into irrelevance.
Hoare Logic - https://en.wikipedia.org/wiki/Hoare_logic
However, they were not just concurrent, but also communicating.
An older gentleman stood up and politely mentioned they knew a thing or two.
That was Tony Hoare.
RIP Sir Tony.
My favourite quote of his is “There are two ways of constructing a piece of software: One is to make it so simple that there are obviously no errors, and the other is to make it so complicated that there are no obvious errors.”
While we hope it's not true, if it is a very deserved RIP.
He famously gave up on making formal methods mainstream, but I believe there will be a comeback quite soon.
On generated code, verification is the bottleneck. He was right, just too early.
(Software) Transactional Memory and other ideas inspired by databases have a much better shot at this.
Tony Hoare was on my bucket list of people I wanted to meet before I or they die. My grad school advisor always talked of him extremely highly, and while I cannot seem to confirm it, I believe Hoare might have been his PhD advisor.
It's hard to overstate how important Hoare was. CSP and Hoare Logic and UTP are all basically entire fields in their own right. It makes me sad he's gone.
I had no idea that a discussion between the three of them even existed.
If I remember correctly he had two immediate ideas, his first was bubble sort, the second turned out to be quicksort.
He was already very frail by then. Yet clarity of mind was undiminished. What came across in that talk, in addition to his technical material, was his humor and warmth.
(Source: TFA)
If I remember correctly, his talk was about how the world of science-the pure pursuit of truth-and the world of engineering-the practical application of solutions under constraints-had to learn from each other.
I always liked this presentation. I think it's equally fine to say "invented" something, but I think this fits into his ethos (from what I understand of him.) There are natural phenomena, and it just takes noticing.
Makes me think of an anecdote where Dijkstra said that he feared he would only be remembered for his shortest path algorithm.
I genuinely forget he authored quicksort on the regular.
Mr. Hoare did a talk back during my undergrad and for some reason despite totally checked out of school I attended, and it is one of my formative experiences. AFAICR it was about proving program correctness.
After it finished during the Q&A segment, one student asked him about his opinions about the famous Brooks essay No Silver Bullet and Mr. Hoare's answer was... total confusion. Apparently he had not heard of the concept at all! It could be a lost in translation thing but I don't think so since I remember understanding the phrase "silver bullet" which did not make any sense to me. And now Mr. Hoare and Dr. Brooks are two of my all time computing heroes.
Edit: Oh and he has multiple honorary doctorates (at least 6!), so would be just as much "Dr." too!
That the death of Sir Tony Hoare has been completely ignored by mainstream news is one of them.
Not a peep anywhere for a man that put a big dent in reality.
> Another good example of recursion is quicksort, a sorting algorithm developed by C.A.R. Hoare in 1962. Given an array, one element is chosen and the others partitioned in two subsets - those less than the partition element and those greater than or equal to it. The same process is then applied recursively to the two subsets. When a subset has fewer than two elements, it doesn't need any sorting; this stops the recursion.
> Our version of quicksort is not the fastest possible, but it's one of the simplest. We use the middle element of each subarray for partitioning. [...]
It was one of the first few 'serious' algorithms I learnt to implement on my own. More generally, the book had a profound impact on my life. It made me fall in love with computer programming and ultimately choose it as my career. Thanks to K&R, Tony Hoare and the many other giants on whose shoulders I stand.
"A consequence of this principle is that every occurrence of every subscript of every subscripted variable was on every occasion checked at run time against both the upper and the lower declared bounds of the array. Many years later we asked our customers whether they wished us to provide an option to switch off these checks in the interests of efficiency on production runs. Unanimously, they urged us not to they already knew how frequently subscript errors occur on production runs where failure to detect them could be disastrous. I note with fear and horror that even in 1980 language designers and users have not learned this lesson. In any respectable branch of engineering, failure to observe such elementary precautions would have long been against the law."
-- C.A.R Hoare's "The 1980 ACM Turing Award Lecture"
His presentation on his billion dollar mistake is something I still regularly share as a fervent believer that using null is an anti-pattern in _most_ cases. https://www.infoq.com/presentations/Null-References-The-Bill...
That said, his contributions greatly outweigh this 'mistake'.
Without things like null pointers, goto, globals, unsafe modes in modern safe(r) languages you can get yourself into a corner by over designing everything, often leading to complex unmaintainable code.
With judicious use of these anti-patterns you get mostly good/clean design with one or two well documented exceptions.
SIR_TONY_HOARE = μX • (think → create → give → X)
-- process ran from 1934 to 2026 -- terminated with SKIP -- no deadlock detected -- all assertions satisfied -- trace: ⟨ quicksort, hoare_logic, csp, monitors, -- dining_philosophers, knighthood, turing_award, -- billion_dollar_apology, structured_programming, -- unifying_theories, ... ⟩ -- trace length: ∞ The channel is closed. The process has terminated. The algebra endures.
> On the topic of films, I wanted to follow up with Tony a quote that I have seen online attributed to him about Hollywood portrayal of geniuses, often especially in relation to Good Will Hunting. A typical example is: "Hollywood's idea of genius is Good Will Hunting: someone who can solve any problem instantly. In reality, geniuses struggle with a single problem for years". Tony agreed with the idea that cinema often misrepresents how ability in abstract fields such as mathematics is learned over countless hours of thought, rather than - as the movies like to make out - imparted, unexplained, to people of 'genius'. However, he was unsure where exactly he had said this or how/why it had gotten onto the internet, and he agreed that online quotes on the subject, attributed to him, may well be erroneous.
Somewhat off-topic, but it's cool hearing this from someone who's contributed so much to the fields of programming and mathematics. It makes me hopeful that my own strugglings with math will pay out over time!
It had intrigued me due to its promise of designing lock-free concurrent systems, that can (I think) also be proven to be deadlock-free.
You do this by building a simple concurrent block that is proven to work correctly, and then build bigger ones using the smaller, proven blocks, to create more complex systems.
The way it is designed is processes don't share data and don't have locks. They use synchronized IPC for passing and modifying data. It seemed to be a foundational piece for designing reliable systems that incorporate concurrency in them.
he read the algol 60 report (Naur, McCarthy, Perlis, …)
and that described "recursion"
=> aaah!
https://www.infoq.com/presentations/Null-References-The-Bill...
In the 60s inventing one single algorithm with 10 lines of code was a thing.
If you did that today nobody would bat an eye.
Today people write game engines, compilers, languages, whole OS and nobody bats an eye cause there are thousands of those.
Quick sort isn't even a thing for leet code interviews anymore because it's not hard enough.
Virtual HLF 2020 – Scientific Dialogue: Sir C. Antony R. Hoare/Leslie Lamport
Just one word: Quicksort.
One-of-a-kind genius.
When I started university he gave a talk to all the new CompScis which as you can imagine was incredibly inspirational for an aspiring Software Engineer.
Grateful to have had that experience.
RIP
Can anyone suggest a better approach for a situation like this in the future? What's better than exposing addressing the problem with a light solution?
https://blog.ploeh.dk/2015/04/13/less-is-more-language-featu...
Null pointers are a software abstraction, and nowadays we have better abstractions.
See the "preface" for details of the book - https://dl.acm.org/doi/10.1145/3477355.3477356
Review of the above book - https://www.researchgate.net/publication/365933441_Review_on...
Somebody needs to contact ACM and have them make the above book freely available now; there can be no better epitaph.
2) Tony Hoare's lecture in honour of Edsger Dijkstra (2010); What can we learn from Edsger W. Dijkstra? - https://www.cs.utexas.edu/~EWD/DijkstraMemorialLectures/Tony...
Somebody needs to now write a similar one for Hoare.
Truly one of the absolute greats in the history of Computer Science.
> The central feature of Hoare logic is the Hoare triple. A triple describes how the execution of a piece of code changes the state of the computation. A Hoare triple is of the form {P}C{Q} where P and Q. are assertions and C is a command.
> P is named the precondition and Q the postcondition: when the precondition is met, executing the command establishes the postcondition. Assertions are formulae in predicate logic.
> Hoare logic provides axioms and inference rules for all the constructs of a simple imperative programming language.
[...]
> Partial and total correctness
> Using standard Hoare logic, only partial correctness can be proven. Total correctness additionally requires termination, which can be proven separately or with an extended version of the While rule
One Day
- Software will be the most reliable component of every product which contains it.
- Software engineering will be the most dependable of all engineering professions.
-Because of the successful interplay of research:
- into the science of programming;
- and the engineering of software.
RIP good sir
Turing Award Legend.
-- process ran from 1934 to 2026 -- terminated with SKIP -- no deadlock detected -- all assertions satisfied -- trace: ⟨ quicksort, hoare_logic, csp, monitors, -- dining_philosophers, knighthood, turing_award, -- billion_dollar_apology, structured_programming, -- unifying_theories, ... ⟩ -- trace length: ∞ The channel is closed. The process has terminated. The algebra endures.
Thank you for your work on ALGOL, you were multiple decade ahead of your time.
Rest in peace.
The idea of 'genius' or in fact 'intelligence' being about speed isn't just a Hollywood thing though; it's also been a Silicon Valley thing as well; it's why most big tech interviews are time-constrained.
Over the years, I've also heard many tech CEOs say stuff alongside "There's only one type of intelligence" or "All intelligent people are intelligent in the same way."
These kinds of statements raised my eyebrows but now with LLMs being able to solve most puzzle problems rapidly but struggling with complex problems it's completely obvious that it's not the case.
What it says is frightening. The CEOs of big companies have been giving positions to people who have the same thinking style as them. Quick puzzle-solving tech tests are literal discrimination against the neurodivergent and also against geniuses. They've been embracing wordcels and rejecting shape rotators.
I think a guy like Tony Hoare would struggle to find a job these days.
You could argue that the issue extends beyond Hollywood and Silicon Valley... The whole education system is centered around puzzle-solving speed. It's hilarious that AI is now solving all these tests within minutes with better scores than humans. Crazy to think that LLMs could graduate from university based on current assessment policies! It's very revealing of what kind of education system we have.
249 points by nextos 16 hours ago | 61 comments
This is how you remind me of what I really am This is how you remind me of what I really am
It's not like you to say sorry I was waitin' on a different story This time I'm mistaken For handing you a heart worth breakin' And I've been wrong, I've been down Been to the bottom of every bottle These five words in my head Scream, "Are we havin' fun yet?"
Yet, yet, yet, no, no Yet, yet, yet, no, no
It's not like you didn't know that I said, "I love you," and I swear I still do And it must have been so bad 'Cause livin' with me must have damn near killed you
And this is how you remind me of what I really am This is how you remind me of what I really am
It's not like you to say sorry I was waitin' on a different story This time I'm mistaken For handing you a heart worth breakin' And I've been wrong, I've been down Been to the bottom of every bottle These five words in my head Scream, "Are we havin' fun yet?"
Yet, yet, yet, no, no Yet, yet, yet, no, no Yet, yet, yet, no, no Yet, yet, yet, no, no
Never made it as a wise man I couldn't cut it as a poor man stealin' And this is how you remind me This is how you remind me
This is how you remind me of what I really am This is how you remind me of what I really am
It's not like you to say sorry I was waitin' on a different story This time I'm mistaken For handing you a heart worth breakin' And I've been wrong, I've been down Been to the bottom of every bottle These five words in my head Scream, "Are we havin' fun yet?"
Yet, yet, are we havin' fun yet? Yet, yet, are we havin' fun yet? Yeah, yeah (These five words in my head scream) Are we havin' fun yet? Yeah, yeah (These five words in my head) No, no