Jules Hedges has written a thought-provoking blog post, On compositionality where he connects the familiar idea of compositionality to the idea of emergent effects in nature, where systems can be understood as either having compositional properties or emergent properties.

The key point about emergent systems is that they are hard to understand, and this is as true for engineering as it is for science. He goes on to say "As a final thought, I claim that compositionality is extremely delicate, and that it is so powerful that it is worth going to extreme lengths to achieve it", so that avoiding emergent effects is a characteristic of good programming language design.

Some thoughts:

1. His examples of emergent systems are biology and game theory from an economic perspective. I would add to this list physics: of his co-authored paper showing that the spectral gap is undecidable, David Pérez-García said "For example, our results show that adding even a single particle to a lump of matter, however large, could in principle dramatically change its properties."
2. Spolsky's famous characterisation of interfaces built on shaky foundations as Leaky abstractions to me makes the distinction between compositional and emergent systems a little less than sharp.
3. We could talk endlessly about the list of what he regards as compositionality-breaking features of PLs. The evils of global state are well-documented, but I find dmbarbour's argument that Local state is poison a very interesting alternative way to look at what properties do we want from code; more generally, what kind of compositionalty PLs offer is very much paradigm dependent. Gotos are considered harmful, but the Linux kernel has little trouble with longjmp because of its mandated coding style: compositionality in engineering is a not just a matter of semantics but also of use. He targets OO and Haskell's type classes - I think he is quite correct - note that within these paradigms one can regain compositionality by restricting to LSP or algebraic classes, and supporting his thesis we see that these ideas have spawned ideas for the design of new, cleaner PLs.

A new introductory book about dependent types, involving some familiar names:

The Little Typer

by Daniel P. Friedman and David Thrane Christiansen.

Foreword by Robert Harper.

Afterword by Conor McBride.

An introduction to dependent types, demonstrating the most beautiful aspects, one step at a time.

A program's type describes its behavior. Dependent types are a first-class part of a language, and are much more powerful than other kinds of types; using just one language for types and programs allows program descriptions to be as powerful as the programs they describe. The Little Typer explains dependent types, beginning with a very small language that looks very much like Scheme and extending it to cover both programming with dependent types and using dependent types for mathematical reasoning. Readers should be familiar with the basics of a Lisp-like programming language, as presented in the first four chapters of The Little Schemer.

The first five chapters of The Little Typer provide the needed tools to understand dependent types; the remaining chapters use these tools to build a bridge between mathematics and programming. Readers will learn that tools they know from programming—pairs, lists, functions, and recursion—can also capture patterns of reasoning. The Little Typer does not attempt to teach either practical programming skills or a fully rigorous approach to types. Instead, it demonstrates the most beautiful aspects as simply as possible, one step at a time.

Seven Sketches in Compositionality: An Invitation to Applied Category Theory

2018 by Brendan Fong and David I. Spivak

Category theory is becoming a central hub for all of pure mathematics. It is unmatched in its ability to organize and layer abstractions, to find commonalities between structures of all sorts, and to facilitate communication between different mathematical communities. But it has also been branching out into science, informatics, and industry. We believe that it has the potential to be a major cohesive force in the world, building rigorous bridges between disparate worlds, both theoretical and practical. The motto at MIT is mens et manus, Latin for mind and hand. We believe that category theory—and pure math in general—has stayed in the realm of mind for too long; it is ripe to be brought to hand.

A very approachable but useful introduction to category theory. It avoids the Scylla and Charybdis of becoming incomprehensible after page 2 (as many academic texts do), and barely scratching the surface (as many popular texts do).

An enjoyable 25-minute introductory talk: YOW! Lambda Jam 2019 - Ken Scambler - Applied Category Theory (slides)

What do programming, quantum physics, chemistry, neuroscience, systems biology, natural language parsing, causality, network theory, game theory, dynamical systems and database theory have in common?

As functional programmers, we know how useful category theory can be for our work - or perhaps how abstruse and distant it can seem. What is less well known is that applying category theory to the real world is an exciting field of study that has really taken off in just the last few years. It turns out that we share something big with other fields and industries - we want to make big things out of little things without everything going to hell! The key is compositionality, the central idea of category theory.

Previously: Seven Sketches in Compositionality: An Invitation to Applied Category Theory.

(via Brian McKenna)

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Michigan football coach Jim Harbaugh penned a two-page open letter advocating flexibility for college athletes looking to enter the NFL Draft.

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As Thailand's capital cautiously reopens many restaurants shuttered over coronavirus fears, the feline "employees" of the Caturday Cafe are back at work.

It was inspired by her current habit of wearing old sweatshirts and sweatpants left behind by childhood friends. READ MORE...

In Special Relativity relativity of simultaneity is the fact that 2 simultaneous events occurring in a stationary frame does not appear simultaneous in a moving frame. For example, in Einstein’s train thought experiment 2 simultaneous flashes of light on the platform do not appear simultaneous for the observer in the train. But relativity of simultaneity...

Michael McEwan speaks to Chris Creegan, Chief Executive of the Scottish Commission for Learning Disability (SCLD) about Learning Disability Week 2017.

The theme for this year is: 'Looking back, thinking forward', which will celebrate achievements, ask searching questions about what needs to happen going forward, and engage the general public on the subject, in the hope of changing attitudes. Chris also gives us some information on SCLD - its ambitions, and current and future focus.

What's on over Learning Disability Week.

Transcript of episode

Music Credit: Something Elated by Broke For Free

As part of Learning Disability Week 2017, we held a roundtable discussion on the topic of parents with learning disabilities to coincide with the launch of our new Iriss Insight on the topic. The discussion highlights how best we can support families where one or both parents have learning disabilities, raises awareness of the key issues, and promotes debate and progress.

It involved Bianca Wood, People First Scotland; Gillian McIntyre, University of Strathclyde; Andy Miller, Policy and Implementation Officer at Scottish Commission for Learning Disability (SCLD); Amanda Muir, Development Manager at Equal Say; and David Barr, Assistant Director at Aberlour.

Bianca is chairperson of the People First (Scotland) Parents' Group, a self-advocacy group of parents with learning disabilities.

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Music Credit: Something Elated by Broke For Free

Michael McEwan speaks to Ryan Fleming about growing up with a 'hidden disability'.

Ryan is on the autistic spectrum and tells us about the challenging, as well as positive experiences he has faced from childhood right through to adulthood.

He talks about how he sees the world, how he interacts in social situations, his support network and his hopes for the future.

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Music Credit: Something Elated by Broke For Free

Michael McEwan speaks to Joseph Delaney about growing up with a 'hidden disability'.

Joseph is on the autistic spectrum and tells us about his life experiences, and his journey to getting his music degree at university and working at Limelight Music.

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Music Credit: Something Elated by Broke For Free

Paisley Disability Resource CentreThe Paisley Disability Resource Centre actively promotes independent living through various leisure, social, educational and employment activities and services. It aims to be a welcoming, supportive and inclusive place, where people come to socialise and network, as well as taking part in activities.

Michael McEwan speaks to Kevin Cantwell, the arts group facilitator at the Centre, as well as a number of people who take part in the activities which include painting, photography and dancing.

Transcript of episode

Music Credit: Something Elated by Broke For Free

The Paisley Disability Resource Centre actively promotes independent living through various leisure, social, educational and employment activities and services. It aims to be a welcoming, supportive and inclusive place, where people come to socialise and network, as well as taking part in activities.

In this second of two episodes, Michael McEwan speaks to Jim Thompson, the web design and movie maker co-ordinator, as well as Duncan Tomlinson, a participant in the activities.

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Music Credit: Something Elated by Broke For Free

Learning Disability Week will take place from 14 to 20 May 2018.

Michael McEwan speaks to Linda Mitchell from the Scottish Commission for Learning Disability (SCLD) about the week's activities.

Transcript of episode

Music Credit: Something Elated by Broke For Free

Our roving reporter on disability issues, Michael McEwan, attended a number of events over Learning Disability Week 2018 (14-20 May) and spoke to the organisers.

We hear about 'Be the Change' campaign created by Enable Scotland, Project Ability and Mind the Gap theatre performance organised by the Scottish Commission for Learning Disability (SCLD).

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Music Credit: Make your dream a reality by Scott Holmes

Michael McEwan speaks to Ethan Young, Civic Participation Officer at Inclusion Scotland about Access to Politics, a project which aims to support disabled people into politics.

Transcript of episode

Music Credit: Make your dream a reality by Scott Holmes