Currently preparing Programming Language Pragmatics slides on JavaScript's prototype-based object model. Teaching interesting object models gives me joy!

A recursive type is a type that has references to other objects of the same type. Recursive types support heap data structures like lists and trees. Learn about recursive types in different languages and how typechecking works in my latest Programming Language Pragmatics video!

Lots of folks captioning aurora photos like "for a few minutes we didn't think about politics" guess I'm built different, every time I'm out trying to see night sky stuff I frequently think about how much light pollution is entirely preventable with just a tiny bit of regulation

Some people say live captioning in talks are like "curb cuts"--an accessibility improvement that helps everyone. Except it doesn't! It actively harms some people (including me).

Had a great time hosting MSE Game Night last night. We played Mysterium, Code Names, RoboRally, Dominion, Kingdomino, and Power Grid. Thanks to everyone who came out (40+ Master of Software Engineering students), you made it fun!

“I want you to understand what it is like to live in Chicago during this time.” aphyr.com/posts/397-i-...

Pointers are dangerous, yet powerful! Languages provide them to support linked data structures and to provide efficient access to objects on the stack. Check out my latest Programming Language Pragmatics video, which talks about pointers and their static and dynamic semantics.

How do arrays work? My latest Programming Language Pragmatics video talks about layout options for multidimensional arrays, array slices, and index computations. I also talk about built-in string and set datatypes, including super-cool bit vector representations. Check it out!

Maduro stole the last election in Venezuela. By all rights he should be deposed. But should the US do it? www.journalofdemocracy.org/articles/how...

Halloween 2025 - Claire and Jamie!

Unions are data types that can hold one of several different representations at run time - allowing you to represent data structures with different variants, or in systems code, interpret the same bytes in two different ways. Learn all about unions in my latest Programming Language Pragmatics video!

FBI: "We didn't zip tie children." REPORTER: "Here's a photo of a zip tied 14 year old." FBI" "OK, we didn't zip tie YOUNG children."

How to records work in programming languages? My latest Programming Language Pragmatics video covers it all: record syntax, operations, semantics, (sub)typing, and run time layout! PLP 8.1: Records - youtu.be/qgG555CJPmM

Great article from @publicsource.org on how campus policy at CMU has shifted against free speech. First limits on "unregistered" speech events at CMU, now possible limits on what students can write on The Fence. Free speech is precious & worth protecting! www.publicsource.org/cmu-expressi...

How can we reuse one function with multiple types? Polymorphism! My latest Programming Language Pragmatics video covers polymorphic (generic) types: type checking, implementation strategies, type constrains, and polymorphic type inference.

How do we check that types are compatible in a program? My latest Programming Language Pragmatics video talks about type compatibility and structural vs. name equivalence, as well as coercions and how to insert them.

Chatbots — LLMs — do not know facts and are not designed to be able to accurately answer factual questions. They are designed to find and mimic patterns of words, probabilistically. When they’re “right” it’s because correct things are often written down, so those patterns are frequent. That’s all.

Is it weird that I don't care about this? I have no attachment to the old East Wing. The public doesn't see it. Every president renovates/remodels some. Trump's changes are kind of chintzy, but the next president will probably fix most of that. A ballroom will probably be useful. So...big shrug?

Watch this. Open your eyes to this brutality. ICE beats up, drags & abducts this disabled visually impaired man. Now share this. Everyone must see the brutality of this administration & ask themselves what they are doing to push back. You have power. Even sharing this video exerts that power.

Went to a prayer service tonight at St. Mary of the Lake, where they have cardboard cutouts throughout the church representing parishioners afraid to come to Mass because of ICE.

What is a type? My new Programming Language Pragmatics video discusses denotational, structural, and behavioral views of typing, demystifies terminology, talks about why types are useful, and introduces subtyping. PLP 7.1: Type Systems - youtu.be/jjYg8aNAYOY

What iteration and recursion constructs do programming languages provide, and how are they implemented? In my latest Programming Language Pragmatics video, I talk about constructs from while loops through generators to tail-recursive functions, along with implementation approaches and tradeoffs.

Information flow is central to security & many other forms of reasoning. But information flow types can be complex in practice. At OOPSLA, Hemant presented a new foundation for information flow types: "Structural Information Flow: A Fresh Look at Types for Non-Interference"

Looks like fun, I'm planning to join!

Why don't we write programs with goto in high level languages anymore? My latest Programming Language Pragmatics video talks about how structured control flow constructs for sequencing and selection replaced more primitive constructs to help make programs more understandable.

This! It's so annoying when transit systems have their own special card or whatever. The ones where you just tap a credit card (like Singapore, where I am this week) are awesome!

How do programming languages define control flow? In my latest Programming Language Pragmatics video, I talk about precedence, order of evaluation, and expression vs. statements. Control flow matters most for side effects; I talk about tradeoffs involved and forms of assignment.

Durian! With sticky rice and coconut milk.

#GradualVerification helps developers specify code one component at a time, checking statically where possible and dynamically where necessary. Come see doubleheader talks on #GradualVerification in #IWACO at #SPLASH 2025 / @icfp-conference.bsky.social! 16:25-17:15 in Peony room 4412.

#LiquidTypes are a lightweight way to specify and check code properties. What stands in the way of more widespread adoption? Today at #SPLASH 2025 / @icfp-conference.bsky.social: @catarinavgamboa.bsky.social will re-present our #PLDI2025 paper on Usability Barriers for Liquid Types.

How does one write efficient code for modern processors? My new Programming Language Pragmatics video covers a big part of the answer: using instruction scheduling and register allocation to reduce pipeline stalls that compromise performance!

Achievement unlocked: was recognized as "the guy who does the programming languages videos" 😀

What instructions do modern processors support? What can you express with them? And how are processors implemented to execute them efficiently? Get a high-level overview in my latest Programming Language Pragmatics video!

How is data represented in computer architectures? My latest Programming Language Pragmatics video gives compiler writers information about twos-complement integers, floating point numbers, and little-endian vs. big-endian byte order, useful for manipulating data in target code.

Went to fill out a recommendation letter request and THE LINK HAD EXPIRED! OMG, this is TERRIBLE policy. The link had to be regenerated by the student, and what if it's the day it's due and there's no time for a round-trip? Actually punishes the most responsible students, who send links early.

Now ICE is shooting praying priests with pepper balls. And MAGA is supposed to be pro-Christianity?

Language implementers need a solid grounding in processor architecture in order to understand how to generate good code. In my latest Programming Language Pragmatics video, I put on my "architecture hat" to cover the memory hierarchy and explain the implications for code generation.

“Terrible things are happening outside. Poor helpless people are being dragged out of their homes. Families are torn apart. Men, women, and children are separated. Children come home from school to find that their parents have disappeared.” Diary of Anne Frank January 13, 1943

How do we know that the semantics of a programming language are right? My latest Programming Language Pragmatics video covers type soundness: the static and dynamic semantics of a language fit together, so that if a program type checks, it will not experience unexpected type errors when it runs.

Check out "You Better Know," the latest dance visual by my eldest, Seal Aldrich! www.youtube.com/watch?v=KIUh...

In addition to checking for typing and other errors, semantic analysis may transform the representation of the program. In today's Programming Language Pragmatics video, I describe how one such transformation, the constant propagation optimization, can be specified using rewriting rules.

In celebration of #HispanicHeritageMonth, ACM is highlighting Trilce Estrada. Trilce Estrada is an Associate Professor and Director of the Data Science Laboratory at the University of New Mexico. Her interests are machine learning, big data and their applications to interdisciplinary problems.

It's *actually* a good plan! I hope, for the sake of Gazans, Israelis, and the world, that it works. www.aljazeera.com/news/2025/9/...

Many organizations are changing their language and policies surrounding DEI. The ACM has not, we are sticking to our principles. - Yannis Ioannidis, ACM president, today I'm proud to be a member & volunteer for the @acm.org!

Interested in taking your software development career to the next level? I'm hosting an information session for CMU's Master of Software Engineering programs this Wednesday October 1st, 1pm EDT. We focus on training leaders in SE, and our graduates' records prove that it works!🧵

How does one implement a type checker? My latest Programming Language Pragmatics video discusses how a type checker, like an interpreter, traverses the AST of a program, implementing the functionality of the typing rule for each AST form.

Ever wonder where Peter, Susan, Edmund, and Lucy lived before the war and Narnia? I think I found it!

Static type checking is awesome! It can find errors at compile time, ensures that type annotations are correct, and helps generate efficient code. In today's Programming Language Pragmatics video, we formalize type checking for expressions and statements with inference rules. youtu.be/Lv-JlRkk3pY

Variables are one of the most fundamental constructs in programming languages. How do we model their semantics formally? Find out in my latest Programming Language Pragmatics video, where I get Formal🤵‍♂️to discuss Dynamic Semantics for Variables and Statements! PLP 4.3 part 2: youtu.be/X7Nu5zEqQ4Q