Site Discussion

Math.js crashes my iPad

The site math viewer is consistently crashing my iPad; it makes a note that it is trying to load something math.js for awhile before Safari just dies. Either this is an iOS issue, or an iOS + great firewall issue (if the font files aren't hosted locally, they are usually hosted by a blocked-in-china google).

LtU now supports Mathjax

LtU now supports MathJax, which allows the use of TeX markup in posts and comments. Note that only TeX/LaTeX markup is currently supported - the alternate MathML format conflict's with the blog's HTML sanitization.

This enhancement is dedicated to neelk, who most recently suggested this feature just over a year ago.

When I went searching for a bit of Mathjax-compatible LaTeX that was relevant to programming languages, the first good example Google found for me was on Neel's blog:

\newcommand{\judge}[3]{{#1} \vdash {#2} : {#3}}
\newcommand{\letv}[3]{\mathsf{let}\;{#1} = {#2}\;\mathsf{in}\;{#3}}
\rule{\judge{\Gamma}{e}{T(A)} \qquad
\judge{\Gamma, x:A}{e'}{T(C)}}

Copy-pasting the above and making it work immediately made it clear that we're going to need a package of useful macros. But it's a start. Feedback welcome.

Note that MathJax rendering is entirely client-side - if you don't see a well-formatted formula above, check the MathJax browser compatibility page and their FAQ.

How is LtU doing?

I thought it was just summer, but now that fall is here, the site still feels kind of quiet.

Genealogical Diagrams broken link

maybe replace


Links in long topics don't work

I tried to post a link to my posting:

but it just posts a link to the first page of a 2-page discussion and doesn't connect to my posting. Seems broken.

A bug with collapsed views, and some thinking aloud

Steps to reproduce:

a) View a forum topic in a collapsed view, say collapsed threaded.
b) Click on a comment.

A page pops up that looks like the reply page, but it's different. Posting a comment there doesn't reply to the comment you're seeing.

This is the reason for this empty comment of mine. I couldn't see any way to delete the comment after I'd moved it to the right place.

Perhaps it would be less confusing if the form on a comment url replied to that url? That's what HN does. Or we could follow reddit and get rid of that form altogether.


I've been bouncing around between views as a way to make sure I don't miss any comments. What do others do? Does everyone use the global track page? It seems unsatisfying for some reason (partly I keep forgetting it exists). And the asterisks feel unreliable because I'm afraid I navigated away without reading all of them.

"Next Page" comment links not working

Say for example,, it loads the first page, and can't jump to the comment because its on the second page.

solution to the ever narrowing posts problem?

are there any drupal hackers who could somehow fix the ever narrowing text problem? :-)

why inheritence in OOP?

I thinking about the design of the object model of a new programming language, and am leaning away from the idea of inheritance.

As far as my understanding goes, inheritance serves the following purposes:

* re-use of code in the child class by inheriting functionality from parent classes

* helping/enabling polymorphism by creating classes that have similar enough capabilities to make them "compatible" to a greater of lesser extent.

Have I missed anything or got aything wrong? Does anyone know of any language type models that do not use inheritance? Does anyone have a view of the pros & cons of such a model?

I've looked at what has been in Go, and my initial impression is that I like it.

Thanks, Mark.

Annual Peter Landin Seminar: 6 December 2011, 6pm, Covent Garden, London. Speaker: Prof Cliff Jones

(Apologies if you receive multiple copies of this announcement)

Peter Landin Annual Semantics Seminar

6 December 2011

BCS London Offices

First Floor, The Davidson Building
5 Southampton Street


Peter Landin (1930--2009) was a pioneer whose ideas underpin modern computing.
In the the 1950s and 1960s, Landin showed that programs could be defined in
terms of mathematical functions, translated into functional expressions in
the lambda calculus, and their meaning calculated with an abstract mathematical
machine. Compiler writers and designers of modern-day programming languages
alike owe much to Landin's pioneering work.

Each year, a leading figure in computer science will pay tribute to Landin's
contribution to computing through a public seminar. This year's seminar is
entitled "To be or not to be" valid?, and will be given by Professor
Cliff Jones (University of Newcastle) -- see below for abstract


5.15pm Coffee
6 pm Welcome and Introduction
6.05pm Peter Landin Semantics Seminar:

"To be or not to be" valid?

Professor Cliff Jones (University of Newcastle)

7.20pm Close
7.20pm - 8.30pm Drinks Reception


If you would like to attend, please email by
3 December.

Seminar details

"To be or not to be" valid?

Professor Cliff Jones (University of Newcastle)

The problem of reasoning about undefined terms has been "solved" (or
avoided) in a variety of ways. (Think about division by zero - but
undefinedness comes up in many ways in program specifications.) For a
long-time, I've used a non-standard logic (LPF) but few others have
joined this movement because such good tools exist for standard,
classical, logic. At some level, I believe that alternative approaches
are "workarounds". I'll try to show why the workarounds present
problems and report on recent positive ideas for mechanising LPF in a
way whose efficiency is close to that of classical logic. To make the
talk accessible to as wide an audience as possible, I'll place the
ideas in a framework that goes back (if not to Shakespeare, at least)
a long way.

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