I have once again realized that I don't fully understand the semantics of System L.

what's the deal with type schemes? they seem like a hack, but I'm not sure what the canonical replacement is

Who is doing the most exciting work at the intersection of PL and LLMs right now?

Finally figured out the right way to formulate the co-lambda calculus, a language of co-data and higher-order continuations

this is sort of what i'm thinking for functions, for example. still fixing the inference for return types but once i'm done with this, i'll have a really expressive and type-safe way to do macros for TS!

Hey, I wrote a post in my blog comparing Elm and @svelte.dev, I hope you enjoy it! flaviocorpa.com/building-a-n...

does anyone know of any frontend/typescript devs with a side interest in PL/CT?

you may not like it but this is what peak operational semantics looks like

My cartoon for this week’s @newscientist.com

Is there a logical interpretation of kan extensions?

I had the same thought....we found people CLAIMED their opposition to policies that support trans people was "protecting women" from male violence. What really predicted their policy positions? Their dislike of trans people.

biology is immutable

Years of tolerating the 'just asking questions' crowd and all we have to show for it is a comeback of fascism

In the polymorphic lambda calculus, we can encode least and greatest type-level fixpoints using quantifiers Is there an analogous construction for term-level fixpoints?

Does anyone here know contextual operational semantics? I'm trying to implement a calculus that's based on linear proof nets, but they use contextual semantics in a cruicial way, and I just can't get my head around it

i fought this guy in dark souls

If you're wondering what compiler infrastructure would look like in dependent types, check out this blog post. We use this library for the development of our language Jermaine at Glaive cybercat.institute/2025/03/13/c...

Is there ever a use-case for needing untagged unions rather than sum types?

Very excited to present my take on bidirectional typing at MSP this Monday coming! We can use polarity and chirality (duality between producers and consumers) to develop a canonical bidirectional typing discipline that requires minimal annotations. msp.cis.strath.ac.uk/msp101.html

is there a reference for combining bidirectional type-checking with unification? ie the bidi system infers most of the types, while the unification only fills in the type-annotations?

Transactions in Category Theory 2025 jademaster.xyz/TACT25.html It's going to be a thing.

Discovered a gem of a paper, which merges two things I am very excited about: DeepRL + (dependently) type-directed program search. Highly recommended read. https://arxiv.org/abs/2407.00695

yeah, I dont think AI is coming for your job any time soon

I'm writing a new blog series on practical implementation of substructural type systems, in Idris! The first blog post will look at substructural polymorphism and why it's *hard*, harder than people assume on first glance! zanzix.github.io/posts/5-subs...

I see people saying this sort of thing often, and quite frankly it makes me sad. The truth is, more people are making good adventure games now than were ever made during the “golden age” of the 90s. For example: 🧵

Twitter was always overrun by dumb people, but now it's overrun by dumb people who are *proud* of being dumb, and that's a whole nother level of intolerable

Very proud to announce the Department of Health will now process all requests to change gender designation on birth certificates within three business days. Previously, there was as much as a 10 month wait.

Dependent types. the final frontier. to boldly type what no one has typed before.

does anyone have a non-trivial example of a linearly distributive category that's not compact closed, ie not Rel/Vect/Prof/Span?

Going into a cave with this post and the "you could have invented transformers" one mathstodon.xyz/@dpiponi/113..., won't emerge until I've understood them.

A new chapter in categorical-ML has just dropped: Transformers are *applicative functors*, and we can use this to generalize them beyond matrices glaive-research.org/2025/02/11/G...

What is a quotient? ~ Kevin Buzzard. xenaproject.wordpress.com/2025/02/09/w... #ITP #LeanProver #Math

I seriously think that CatColab is one of the more exciting projects I have seen in the last few years and cannot speak more highly about it! It's thrilling to see the work being done here, how the categorical underpinnings work (double categories!), and it's potential in team-based modeling!

the can't isnt actually alive or dead, it's alive ⅋ dead

It's standard in dependent type theory to implement types and terms as a single judgement, but I wonder what happens if you don't do that. It'd be a more restrictive system, but perhaps interesting in its own way

is there a nice inductive definition of "lists indexed by an upper-bound on their length"?

Hot take: record types should be fully determined by their field names and types, and therefore shouldn't need a constructor name This is something that typescript gets right that Haskell and Idris don't

dont you just hate it when you think you have a great idea but the type-checker disagrees

type-checking is a lens!

Traversals are the optics for applicative functors, but is there an optic for alternative functors? forall f. (Alternative f) => (a -> f b) -> s -> f t

americans really love to chastise you for not voting for kamala doesn't even matter if you're not american. "oh, you live in london, and so couldn't vote? don't care, it's *your* fault she lost"

not at POPL myself, but would love to experience it vicariously - send me the coolest ideas you've learned so far

Never forget that you do can do natural gradient descent in Haskell! github.com/alex404/goal

are elm/purescript still as active as ever, or are they past their peak? I feel like I haven't seen jobs in either in qutie some time... Is it that React has eaten their lunch by leaning more into FP over the years?

what're the most exciting topics in the current JS/React/front-end dev meta? whom should i be following?

This has been a long time coming! Have you ever wondered what lenses and UI programming have in common? Can we recreate React, Elm, and Redux entirely using pure category theory? Read this series to find out. cybercat.institute/2025/01/21/u...

A situation that arose in the MSP office yesterday

what is a chili pepper's one weakness? a chili's heel