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

The Trade Review Act of 2025 is a great idea--restoring real Tariff authority to Congress as per the constitution. It gives the president the ability to act quickly if needed, but Congress can cancel tariffs anytime and they expire automatically if not approved within 60 days.

Time to get formal!🤵‍♂️ In today's Programming Language Pragmatics video, I put on my tux (and play Bach!) to talk about defining the meaning of programs. We use math formalism to precisely specify the dynamic semantics of a language: how program expressions evaluate to a value. youtu.be/gJGrVQCBMYs

Let's make the U-Turn happen!

Spoiler: it works!

Where's Maverick when you need him?

How does a compiler construct an abstract syntax tree? My latest Programming Language Pragmatics video describes how action routines can be embedded in the parser to easily construct an AST. PLP 4.2: Constructing Abstract Syntax Trees with Action Routines - youtu.be/2ubaN1wfjQY

This is the top headline on CNN. A good warning sign that your country may be becoming a dictatorship is when your plain-jane straight news networks start saying “Our country is becoming a dictatorship”

In the latest People of ACM, Richa Singh outlines trends in pattern recognition and her role as Co-EiC of "AI Letters," a new ACM journal. She also discuses the impact of generative AI and machine unlearning on her field. Read the interview here:

Q: How do you define the meaning of a program? A: With semantics! How program output is computed from input, and checking of rules. Watch my new Programming Language Pragmatics video, covering dynamic vs. static semantics, & how to represent a program with abstract syntax trees.

Canada signed on to ACM OPEN! I'm super happy, this was worrying to a lot of my Canadian colleagues. Now faculty and students at Canadian universities that are part of the consortia can publish Open Access with ACM with no article processing charges. www.acm.org/media-center...

How do first-class functions look up the value of a variable from an outer scope? Learn about referencing environments, closures, and macros in my latest Programming Language Pragmatics video! PLP 3.6-3.7: Referencing Environments, Closures, and Macros - youtu.be/JBs4dY9nwOY

Solar greening: solar panels improved soil chemistry, moisture retention, and even signs of vegetation recovery. Shading from panels reduces surface heating and evaporation, creating a cooler and more stable microclimate dailygalaxy.com/2025/09/chin...

Modules provide abstraction, hide information, and scope names. In my latest Programming Language Pragmatics video, I talk about the value of modules, how separate compilation relies on modular structure, and discuss related issues such as aliased names and overloaded functions.

Why do some languages require that functions be defined before they are used? When several variables in a program have the same name, which one is used? My latest Programming Language Pragmatics video discusses scoping rules, covers these issues and more! PLP 3.3: Scope Rules - youtu.be/0PhZUc92o4s

How long does a variable live? When is it accessible? How does that relate to where it is stored? My latest video covers these questions and provides a model for lifetimes & storage management in programming languages. PLP 3.2: Object Lifetimes and Storage Management - youtu.be/C07ej-OCugY

What's in a name? Today launches the first video in Chapter 3 of Programming Language Pragmatics, on Names, Scopes, and Binding! Follow along to learn more about that most fundamental of language capabilities: giving things names. Video: youtu.be/BmnfjwneZRw

Introduction to Formal Semantics in class today-- dressing for the occasion!

My Programming Language Pragmatics videos on Syntax have been fun! The latest video closes the series, covering * Connections between parsing techniques and automata theory * Parsing error recovery with panic mode * Generalized LR parsers & Parsing Expression Grammars (PEGs) youtu.be/OHrvh6D9uEk

It's the Caregorical Imperative!

LR parsing is a powerful technique, but natural grammars can still have conflicts--even for expressions as simple as if-then-else. What to do? Find out in my latest Programming Language Pragmatics video! Video: youtu.be/vHkUBM8geOk Programming Language Pragmatics playlist: tinyurl.com/PLP5vids

I’m happy to share that I’m starting a new position as Director, Master of Software Engineering (MSE) Programs at Carnegie Mellon University's Software and Societal Systems Department!

How do bottom-up, LR parsers work? Learn about this powerful and flexible parsing technique in my new Programming Language Pragmatics video! Video: youtu.be/Ct2fLcbFkJM Programming Language Pragmatics playlist: tinyurl.com/PLP5vids

Q: Is it OK to get the references for my paper from generative AI? A: Only if you verify they are real & relevant. Submitting a paper with hallucinated references would violate the ACM Policy on Authorship, and your paper will likely be desk rejected.

How do you implement a top-down parser? Learn two different approaches, recursive descent and table-driven, in my latest Programming Language Pragmatics video! Video: youtu.be/DOHfpWHINTE Programming Language Pragmatics playlist: tinyurl.com/PLP5vids

How do parsers work? Check out my latest Programming Language Pragmatics video for an overview of parsing and a deep dive into top-down parsing techniques! youtu.be/f96oRq3deq4

In programming language syntax, tokens are specified with regular expressions, but scanners are implemented as deterministic finite automaton. How do you go from one to the other? Find out in my latest Programming Language Pragmatics video, Generating a Finite Automaton! youtu.be/aRHQ7c_m2J0

How do compilers and other programming tools read code? For the first part of the story, watch my new Programming Language Pragmatics video on Scanning: reading program text and dividing it into tokens, the smallest units of text that make sense on their own. Video: youtu.be/Xq76NmFDRII

The party of small government is now the party of big brother.

Just ate my first artichoke! Amazing, where have you been all my life?

How can we specify the recursive structure of programming language expressions? Watch my new Programming Language Pragmatics video, "Specifying Syntax: Context-Free Grammars, Derivations and Parse Trees!" Video: youtu.be/xsKoHAX7NHs Programming Language Pragmatics playlist: tinyurl.com/PLP5vids

New video release: Specifying Syntax with Regular Expressions! Unlike natural languages, programming languages must have a precise specification. In this talk we look at how the most basic levels of programming language syntax can be captured with regular expressions. Video: youtu.be/60t3C4BNUY8

What's the difference between compilation and interpretation? Why choose one over the other? Watch the full Compilation, Interpretation, and Environments video to find out: youtu.be/mrmoRheZJus For more details, pick up a copy of our Programming Language Pragmatics text!

New video release: An Overview of Compilation! I talk about the various phases in the front end and back end of the compiler, from scanning and parsing to semantic analysis, code improvement, and target code generation--illustrating what happens in each phase. youtu.be/CD2h20VD3Ow

Why would YOU choose one programming language over another? I talk about programming languages, tradeoffs, and why we study them in my first Programming Language Pragmatics video. Check it out! Full video: www.youtube.com/watch?v=hwL0... Playlist: tinyurl.com/PLP5vids

Want to know more about programming languages? Here's the intro to my first Programming Language Pragmatics talk! Watch the full video on YouTube, then learn more about languages through our textbook and my series of short, accessible videos. Playlist: tinyurl.com/PLP5vids

Released today: the second video in my Programming Language Pragmatics series, covering Compilation, Interpretation, and Environments! www.youtube.com/watch?v=mrmo... Going forward, I'll post a video 3 times a week. Please share the series with anyone who might benefit!

Launching my Programming Language Pragmatics talks! These short, accessible talks cover the material in the textbook, the 5th edition of which I wrote with Michael L. Scott. The first one introduces the topic and talks about why we study programming languages! www.youtube.com/watch?v=hwL0...

The North Cascades from the summit block of Sahale Mountain yesterday. Amazing hike: 13.5 miles, 4000 feet gained, a glacier, meadows, goats, marmots, and peaks as far as the eye could see!

Hiking to Lake Ann yesterday

Building *slows* gentrification; and *not* building makes it much worse: "The findings suggest that not allowing more homes to be built—even for high-income residents—pushes up all rents, making it harder for low-income tenants to remain in their neighborhoods." -- www.pew.org/en/research-...

another model selling jeans. yawn.

Hiking Heliotrope Ridge today

Hiking Yellow Aster Butte today

Common mistake: mixing stylistic improvements with new functionality in a single PR. Makes reviewing the PR very difficult.

Policymakers should accept that the red part of this graph represents brand new, often high end housing and pursue pursue policies that bring down the price of the homes in the blue part.

Join me, sign the petition for free speech at the CMU Fence! Last week during Trump's visit, the CMU administration painted over the students' Fence--censoring student speech there for the first time in its 100-year history. Please sign and share: docs.google.com/forms/d/e/1F...

Two things both true: The loved ones of Venezuelans are celebrating that they are no longer in CECOT; some are celebrating their return home. And. It is a violation of international law to cause someone to be returned where they’ll be persecuted. Most of them never got a chance to make that case.

Bought something heavy from a private seller and paid shipping. It was ASTONISHING how much it costs. Obviously a 2x-4x what Amazon must be paying to ship. I then found Pirate Ship and verified that indeed I had overpaid. CRAZY levels of ripoff. Lesson learned!

Yesterday, Maurene Comey, who prosecuted the Epstein case, was summarily fired from SDNY. Her letter to colleagues pulls no punches. "Fear is the tool of a tyrant, wielded to suppress independent thought." h/t @msnbc.com