Howard on Curry-Howard

Philip Wadler posts his exchange with William Howard on history of the Curry-Howard correspondence. Howard on Curry-Howard.

Interactive scientific computing; of pythonic parts and goldilocks languages

Graydon Hoare has an excellent series of (two) blog posts about programming languages for interactive scientific computing.
technicalities: interactive scientific computing #1 of 2, pythonic parts
technicalities: interactive scientific computing #2 of 2, goldilocks languages

The scenario of these posts is to explain and constrast the difference between two scientific computing languages, Python and "SciPy/SymPy/NumPy, IPython, and Sage" on one side, and Julia on the other, as the result of two different design traditions, one (Python) following Ousterhout's Dichotomy of having a convenient scripting language on top of a fast system language, and the other rejecting it (in the tradition of Lisp/Dylan and ML), promoting a single general-purpose language.

I don't necessarily buy the whole argument, but the posts are a good read, and have some rather insightful comments about programming language use and design.

Quotes from the first post:

There is a further split in scientific computing worth noting, though I won't delve too deep into it here; I'll return to it in the second post on Julia. There is a division between "numerical" and "symbolic" scientific systems. The difference has to do with whether the tool is specialized to working with definite (numerical) data, or indefinite (symbolic) expressions, and it turns out that this split has given rise to quite radically different programming languages at the interaction layer of such tools, over the course of computing history. The symbolic systems typically (though not always) have much better-engineered languages. For reasons we'll get to in the next post.


I think these systems are a big deal because, at least in the category of tools that accept Ousterhout's Dichotomy, they seem to be about as good a set of hybrid systems as we've managed to get so far. The Python language is very human-friendly, the systems-level languages and libraries that it binds to are well enough supported to provide adequate speed for many tasks, the environments seem as rich as any interactive scientific computing systems to date, and (crucially) they're free, open source, universally available, easily shared and publication-friendly. So I'm enjoying them, and somewhat hopeful that they take over this space.

Quotes from the second:

the interesting history here is that in the process of implementing formal reasoning tools that manipulate symbolic expressions, researchers working on logical frameworks -- i.e. with background in mathematical logic -- have had a tendency to produce implementation languages along the way that are very ... "tidy". Tidy in a way that befits a mathematical logician: orthogonal, minimal, utterly clear and unambiguous, defined more in terms of mathematical logic than machine concepts. Much clearer than other languages at the time, and much more amenable to reasoning about. The original manual for the Logic Theory Machine and IPL (1956) makes it clear that the authors were deeply concerned that nothing sneak in to their implementation language that was some silly artifact of a machine; they wanted a language that they could hand-simulate the reasoning steps of, that they could be certain of the meaning of their programs. They were, after all, translating Russel and Whitehead into mechanical form!


In fact, the first couple generations of "web languages" were abysmally inefficient. Indirect-threaded bytecode interpreters were the fast case: many were just AST-walking interpreters. PHP initially implemented its loops by fseek() in the source code. It's a testament to the amount of effort that had to go into building the other parts of the web -- the protocols, security, naming, linking and information-organization aspects -- that the programming languages underlying it all could be pretty much anything, technology-wise, so long as they were sufficiently web-friendly.

Of course, performance always eventually returns to consideration -- computers are about speed, fundamentally -- and the more-dynamic nature of many of the web languages eventually meant (re)deployment of many of the old performance-enhancing tricks of the Lisp and Smalltalk family, in order to speed up later generations of the web languages: generational GC, JITs, runtime type analysis and specialization, and polymorphic inline caching in particular. None of these were "new" techniques; but it was new for industry to be willing to rely completely on languages that benefit, or even require, such techniques in the first place.


Julia, like Dylan and Lisp before it, is a Goldilocks language. Done by a bunch of Lisp hackers who seriously know what they're doing.

It is trying to span the entire spectrum of its target users' needs, from numerical inner loops to glue-language scripting to dynamic code generation and reflection. And it's doing a very credible job at it. Its designers have produced a language that seems to be a strict improvement on Dylan, which was itself excellent. Julia's multimethods are type-parametric. It ships with really good multi-language FFIs, green coroutines and integrated package management. Its codegen is LLVM-MCJIT, which is as good as it gets these days.

Fifty Years of BASIC, the Programming Language That Made Computers Personal

Fifty Years of BASIC, the Programming Language That Made Computers Personal

A very comprehensive history of BASIC from Time magazine.

Invented by John G. Kemeny and Thomas E. Kurtz of Dartmouth College in Hanover, New Hampshire, BASIC was first successfully used to run programs on the school’s General Electric computer system 50 years ago this week–at 4 a.m. on May 1, 1964, to be precise.

Edit: Dartmouth is celebrating Basic at 50.

How I Came to Write D

Walter Bright recounts how he came to write D

The path that led Walter Bright to write a language, now among the top 20 most used, began with curiosity — and an insult.

The Essence of Reynolds

The Essence of Reynolds by Stephen Brookes, Peter O'Hearn and Uday Reddy.

John Reynolds (1935-2013) was a pioneer of programming languages research. In this paper we pay tribute to the man, his ideas, and his influence.

Corresponding presentation from POPL.

Propositions as Types

Propositions as Types, Philip Wadler. Draft, March 2014.

The principle of Propositions as Types links logic to computation. At first sight it appears to be a simple coincidence---almost a pun---but it turns out to be remarkably robust, inspiring the design of theorem provers and programming languages, and continuing to influence the forefronts of computing. Propositions as Types has many names and many origins, and is a notion with depth, breadth, and mystery.

Philip Wadler has written a very enjoyable (Like busses: you wait two thousand years for a definition of “effectively calculable”, and then three come along at once) paper about propositions as types that is accessible to PLTlettantes.

Wirth Symposium

Celebrating Niklaus Wirth's 80th Birthday, 20th Feb 2014.

Niklaus Wirth was a Professor of Computer Science at ETH Zürich, Switzerland, from 1968 to 1999. His principal areas of contribution were programming languages and methodology, software engineering, and design of personal workstations. He designed the programming languages Algol W, Pascal, Modula-2, and Oberon, was involved in the methodologies of structured programming and stepwise refinement, and designed and built the workstations Lilith and Ceres. He published several text books for courses on programming, algorithms and data structures, and logical design of digital circuits. He has received various prizes and honorary doctorates, including the Turing Award, the IEEE Computer Pioneer, and the Award for outstanding contributions to Computer Science Education.

We celebrated Niklaus Wirth's 80th birthday at ETH Zürich with talks by Vint Cerf, Hans Eberlé, Michael Franz, Bertrand Meyer, Carroll Morgan, Martin Odersky, Clemens Szyperski, and Kathleen Jensen. Wirth himself gave a talk about his recent port of Oberon onto a low-cost Xilinx FPGA with a CPU of his own design.

The webpage includes videos of the presentations.

Oral History of Adele Goldberg

Interesting and wide-ranging interview with Adele Goldberg from Computer History
Transcript and Video at Computer History Also on YouTube

Adele Goldberg reflects on her life and career from her early days at the University of Chicago and Stanford University through her career at Xerox Palo Alto Research Center (PARC) and ParcPlace Systems.

Another Oral History interview with her by IEEE Global History Network

Goldberg discusses her educational and work history. She recalls her experiences as a student at the University of Michigan and at the University of Chicago. Next, she covers her stretch at Xeorx PARC, sharing her views on the work environment. Here she speaks at length about her work on Smalltalk, including her leading role in its commercialization. Goldberg is candid about the challenges she faced in forming and running spin-out company ParcPlace Systems. In addition, she discusses her two-year tenure as President of ACM. Finally, Goldberg offers advice for young women who are considering a career in computing.

The origin of zero-based array indexing

An amusing historical analysis of the origin of zero based array indexing (hint: C wasn't the first). There's a twist to the story which I won't reveal, so as not to spoil the story for you. All in all, it's a nice anecdote, but it seems to me that many of the objections raised in the comments are valid.

John C. Reynolds, 1935-2013

Randy Bryant, dean of the school of computer science at CMU, sent out an email saying that John C. Reynolds passed away yesterday.

Subject: In Memoriam. John Reynolds, June 1, 1935 - April 28, 2013
Date: Sun, 28 Apr 2013 21:45:12 -0400
From: Randy Bryant
To: scs-all@cs.cmu.edu

I'm sorry to announce that John Reynolds, a long-time member of our computer science faculty, passed away early this morning. Many of you know that John had been in declining health recently. We were able to celebrate his retirement him last summer. He had a heart attack last week and went downhill over a period of several days.

John got his PhD in 1961 in theoretical physics, but while working at Argonne National Laboratory came to realize that his passion was for computation. He became a very successful computer scientists, focusing on the logical foundations of programs and programming languages. He was at Syracuse University from 1970 to 1986 and then joined the CSD faculty.

John has made many important contributions over his career. Interestingly, his 2002 work on separation logic, done jointly with Peter O'Hearn and others, has been especially prominent. Separation logic provides a formal way to reason about what we might think of as "normal programs," i.e., ones that operate by changing the values stored in memory, but where memory is partitioned into independent blocks, and so we can reason about different program components independently. I can only hope that the work I do at age 67 would be counted among my best!

We will also remember John for this cheerful spirit, his high ethical standards, and his deep intellect. He will very much be missed.

Randy Bryant

It's probably impossible to overstate the impact that John had on the field of programming languages. But beyond being a great scholar, he was also a generous mentor and a fundamentally decent and kind human being. He will indeed very much be missed.

XML feed