Posts tagged research

What is logical relations?

:: research, notes, academia

I have long struggled to understand what a logical relation is. This may come as a surprise, since I have used logical relations a bunch in my research, apparently successfully. I am not afraid to admit that despite that success, I didn’t really know what I was doing—I’m just good at pattern recognition and replication. I’m basically a machine learning algorithm.

So I finally decided to dive deep and figure it out: what is a logical relation?

As with my previous note on realizability, this is a copy of my personal notebook on the subject, which is NOT AUTHORITATIVE, but maybe it will help you.

What is realizability?

:: research, notes, academia

I recently decided to confront the fact that I didn’t know what “realizability” meant. I see it in programming languages papers from time to time, and could see little rhyme or reason to how it was used. Any time I tried to look it up, I got some nonsense about constructive mathematics and Heyting arithmetic, which I also knew nothing about, and gave up.

This blog post is basically a copy of my personal notebook on the subject, which is NOT AUTHORITATIVE, but maybe it will help you.

The A Means A

:: research, academia

I have argued about the definition of “ANF” many times. I have looked at the history and origins, and studied the translation, and spoken to the authors. And yet people insist I’m “quacking” because I insist that “ANF” means “A-normal form”, where the “A” only means “A”.

Here, I write down the best version of my perspective so far, so I can just point people to it.

How I Redex—Experimenting with Languages in Redex

:: research, tutorial

Recently, I asked my research assistant, Paulette, to create a Redex model. She had never used Redex, so I pointed her to the usual tutorials:

While she was able to create the model from the tutorials, she was left the question “what next?”. I realized that the existing tutorials and documentation for Redex do a good job of explaining how to implement a Redex model, but fail to communicate why and what one does with a Redex model.

I decided to write a tutorial that introduces Redex from the perspective I approach Redex while doing work on language models—a tool to experiment with language models. The tutorial was originally going to be a blog post, but it ended up quite a bit longer that is reasonable to see in a single page, so I’ve published it as a document here:

Experimenting with Languages in Redex

Untyped Programs Don’t Exist

:: research

Lately, I’ve been thinking about various (false) dichotomies, such as typed vs untyped programming and type systems vs program logics. In this blog post, I will argue that untyped programs don’t exist (although the statement will turn out to be trivial).


All languages are typed, but may use different enforcement mechanisms (static checking, dynamic checking, no checking, or some combination). We should talk about how to use types in programming—e.g. tools for writing and enforcing invariants about programs—instead of talking about types and type checking as properties of languages.

The reviewers were right to reject my paper

:: academia, research

I submitted two papers to POPL 2018. The first, “Type-Preserving CPS Translation of Σ and Π Types is Not Not Possible”, was accepted. The second, “Correctly Closure-Converting Coq and Keeping the Types, Too” (draft unavailable), was rejected.

Initially, I was annoyed about the reviews. I’ve since reconsidered the reviews and my work, and think the reviewers were right: this paper needs more work.

What even is compiler correctness?

:: research

In this post I precisely define common compiler correctness properties. Compilers correctness properties are often referred to by vague terms such as “correctness”, “compositional correctness”, “separate compilation”, “secure compilation”, and others. I make these definitions precise and discuss the key differences. I give examples of research papers and projects that develop compilers that satisfy each of these properties.

Toward Type-Preserving Compilation of Coq, at POPL17 SRC

:: academia, research

Almost two months ago, my colleagues in the Northeastern PRL wrote about three of our POPL 2017 Student Research Competition submissions. There was fourth submission, but because I was hard at work completing proofs, it wasn’t announced.

Toward Type-Preserving Compilation of Coq

Toward Type-Preserving Compilation of Coq
William J. Bowman

A type-preserving compiler guarantees that a well-typed source program is compiled to a well-typed target program. Type-preserving compilation can support correctness guarantees about compilers, and optimizations in compiler intermediate languages (ILs). For instance, Morrisett et al. (1998) use type-preserving compilation from System F to a Typed Assembly Languages (TAL) to guarantee absence of stuckness, even when linking with arbitrary (well-typed) TAL code. Tarditi et al. (1996) develop a compiler for ML that uses a typed IL for optimizations.

We develop type-preserving closure conversion for the Calculus of Constructions (CC). Typed closure conversion has been studied for simply-typed languages (Minamide1996, Ahmed2008, New2016) and polymorphic languages (Minamide1996, Morrisett1998). Dependent types introduce new challenges to both typed closure conversion in particular and to type preservation proofs in general.

ICFP 2016

:: academia, research

Full disclosure: This blog post is sponsored in part by ACM SIGPLAN. ACM SIGPLAN! Pushing the envelope of language abstractions for making programs better, faster, correcter, stronger.


I went to ICFP again this year. I’m a frequent attendee. Last year I had a paper and gave a talk. This year I had a paper, but someone else gave the talk. But I also gave a talk at HOPE 2016. I met some people and saw some talks and pet a deer.