There's no functor like Hom
September 2, 2025 at 10:14 AM
There's no functor like Hom
so you're telling me this functor is bi?
March 9, 2025 at 3:32 PM
so you're telling me this functor is bi?
ghc is so magical sometimes.
i came accross [this](twanvl.nl/blog/haskell...) really neat blog post earlier, where the FunList data type has a pretty non-obvious Functor instance
but what surprised me was: using `deriving Functor` on this definition just figures it out?? how???
i came accross [this](twanvl.nl/blog/haskell...) really neat blog post earlier, where the FunList data type has a pretty non-obvious Functor instance
but what surprised me was: using `deriving Functor` on this definition just figures it out?? how???
December 15, 2024 at 2:32 AM
ghc is so magical sometimes.
i came accross [this](twanvl.nl/blog/haskell...) really neat blog post earlier, where the FunList data type has a pretty non-obvious Functor instance
but what surprised me was: using `deriving Functor` on this definition just figures it out?? how???
i came accross [this](twanvl.nl/blog/haskell...) really neat blog post earlier, where the FunList data type has a pretty non-obvious Functor instance
but what surprised me was: using `deriving Functor` on this definition just figures it out?? how???
oh so kan extensions are just adjoints of the functor on functor categories induced by functor precomposition my GOD why didn't you just SAY that
June 16, 2026 at 8:13 AM
oh so kan extensions are just adjoints of the functor on functor categories induced by functor precomposition my GOD why didn't you just SAY that
you want me to use less object oriented code here? how about i functor your mom until she monads
September 22, 2026 at 12:55 PM
you want me to use less object oriented code here? how about i functor your mom until she monads
❌ contravariant functor
✅ flippy functor
✅ flippy functor
January 17, 2026 at 5:59 AM
❌ contravariant functor
✅ flippy functor
✅ flippy functor
Well, the functor determines a monad on the category of gun.
March 22, 2025 at 6:15 PM
Well, the functor determines a monad on the category of gun.
se for menina Monada se for menino Functor
November 5, 2025 at 9:45 PM
se for menina Monada se for menino Functor
Maxine Calle (my undergraduate advisee) and @jacksonmorris.bsky.social (my PhD advisee) are both presenting in the Electronic Computational Homotopy Theory seminar next Thursday! Details at echtorc.github.io/echt-researc.... 🧮
September 18, 2026 at 8:47 PM
Maxine Calle (my undergraduate advisee) and @jacksonmorris.bsky.social (my PhD advisee) are both presenting in the Electronic Computational Homotopy Theory seminar next Thursday! Details at echtorc.github.io/echt-researc.... 🧮
Today's arXiv find is a paper proving that spectral sheaves form the initial ∞-category of continuous six functor formalisms on locally compact Hausdorff spaces (arxiv.org/abs/2507.13537).
With love and admiration: Mathematicians must be stopped before the subject ouroborically consumes itself.
With love and admiration: Mathematicians must be stopped before the subject ouroborically consumes itself.
Continuous six-functor formalism on locally compact Hausdorff spaces
We show that the functor sending a locally compact Hausdorff space $X$ to the $\infty$-category of spectral sheaves $\mathrm{Shv}(X; \mathrm{Sp})$ is initial among all continuous six-functor formalism...
arxiv.org
July 21, 2025 at 8:19 PM
Today's arXiv find is a paper proving that spectral sheaves form the initial ∞-category of continuous six functor formalisms on locally compact Hausdorff spaces (arxiv.org/abs/2507.13537).
With love and admiration: Mathematicians must be stopped before the subject ouroborically consumes itself.
With love and admiration: Mathematicians must be stopped before the subject ouroborically consumes itself.
Functor and profunctor always gets me. lol
February 2, 2025 at 1:55 PM
Functor and profunctor always gets me. lol
Last year in a YouTube podcast i said something like “a cat is a functor that maps cat food into shit”
September 19, 2026 at 2:49 AM
Last year in a YouTube podcast i said something like “a cat is a functor that maps cat food into shit”
tl;dr is that exp as a generic type is roughly the functor producing the structure of all finite sets, and the taylor expansion can be viewed as the quotient of the list functor by the action of S_n
April 24, 2026 at 3:19 PM
tl;dr is that exp as a generic type is roughly the functor producing the structure of all finite sets, and the taylor expansion can be viewed as the quotient of the list functor by the action of S_n
"Nathan how would you define a functor?"
"No"
"No"
November 20, 2024 at 3:02 AM
"Nathan how would you define a functor?"
"No"
"No"
Bluesky-ization is left adjoint to the forgetful functor from blue skies to skies.
September 13, 2025 at 10:36 PM
Bluesky-ization is left adjoint to the forgetful functor from blue skies to skies.
Another great feature that still seems stuck is "include functor". It's also been hugely popular internally. I see it showing up 43k times in our internal repo! I'd love to see that get in as well.
github.com/ocaml/RFCs/p...
github.com/ocaml/RFCs/p...
`include functor` by ccasin · Pull Request #43 · ocaml/RFCs
This is a proposal for a new structure and signature item form, include functor.
Rendered version
(Thanks to @OlivierNicole and @goldfirere for help preparing this RFC)
github.com
February 23, 2025 at 2:11 PM
Another great feature that still seems stuck is "include functor". It's also been hugely popular internally. I see it showing up 43k times in our internal repo! I'd love to see that get in as well.
github.com/ocaml/RFCs/p...
github.com/ocaml/RFCs/p...
This will remove so many unnecessary OCaml functors from our codebases. My rough rule of thumb is that if a functor is not applied more than once in a codebase, it doesn’t need to be a functor. Parameterised libraries lets us easily do one-shot reuse of existing modules in a different context.
We've finally landed a full version internally (coming to an OxCaml near you soon!) of a new feature called parameterized libraries.
It's basically an answer to a problem I first ran into 23 years ago. Here's a thread about it on the caml-list.
inbox.vuxu.org/caml-list/10...
It's basically an answer to a problem I first ran into 23 years ago. Here's a thread about it on the caml-list.
inbox.vuxu.org/caml-list/10...
[Caml-list] Functorizing large collections of modules - Yaron M. Minsky
inbox.vuxu.org
August 7, 2025 at 6:09 AM
This will remove so many unnecessary OCaml functors from our codebases. My rough rule of thumb is that if a functor is not applied more than once in a codebase, it doesn’t need to be a functor. Parameterised libraries lets us easily do one-shot reuse of existing modules in a different context.
Have no clue what a functor is but I should learn Haskell
February 3, 2026 at 2:22 AM
Have no clue what a functor is but I should learn Haskell
canonical class Functor[*(rf : Rep :-> Rep)](*f : forall *(r : Rep). Type(r) :-> Type(rf(r)))
declarations dreamed up by the utterly deranged
declarations dreamed up by the utterly deranged
May 20, 2026 at 12:34 PM
canonical class Functor[*(rf : Rep :-> Rep)](*f : forall *(r : Rep). Type(r) :-> Type(rf(r)))
declarations dreamed up by the utterly deranged
declarations dreamed up by the utterly deranged
Very tempted to tell my combinatorics students how a directed graph is a span V←E→V (source, target) and its adjacency matrix is its image under the usual functor Span(FinSet)→Mat_ℕ.
September 14, 2026 at 3:12 AM
Very tempted to tell my combinatorics students how a directed graph is a span V←E→V (source, target) and its adjacency matrix is its image under the usual functor Span(FinSet)→Mat_ℕ.
Modern math education (inclusive of discrete math, type theory, etc) is gonna be so important *because* it will allow you to articulate very large concepts very succinctly.
Sort of the way "functor", "applicative functor" and "monad" are modern power words for defining architecture.
Sort of the way "functor", "applicative functor" and "monad" are modern power words for defining architecture.
it's 2026 you can just say "reiter snowflake but on a pentagonal poincare disk :3 static html minimal deps pls" and the computer will simply whip up a reiter snowflake model on a hyperbolic pentagon tiling
June 8, 2026 at 5:43 PM
Modern math education (inclusive of discrete math, type theory, etc) is gonna be so important *because* it will allow you to articulate very large concepts very succinctly.
Sort of the way "functor", "applicative functor" and "monad" are modern power words for defining architecture.
Sort of the way "functor", "applicative functor" and "monad" are modern power words for defining architecture.
using the vertification functor to turn my preverts into verts
November 30, 2025 at 8:04 PM
using the vertification functor to turn my preverts into verts
NEWS: We don't say functor anymore in the #ReScript ecosystem.
OCaml's notion of a functor is not the one from category theory, it is a higher-order module.
So we simply settled for "module function".
Furthermore we have documented them properly now. Thank you, @vlkpack.com!
OCaml's notion of a functor is not the one from category theory, it is a higher-order module.
So we simply settled for "module function".
Furthermore we have documented them properly now. Thank you, @vlkpack.com!
Module Functions | ReScript Language Manual
Module Functions in ReScript
rescript-lang.org
November 26, 2024 at 5:05 PM
NEWS: We don't say functor anymore in the #ReScript ecosystem.
OCaml's notion of a functor is not the one from category theory, it is a higher-order module.
So we simply settled for "module function".
Furthermore we have documented them properly now. Thank you, @vlkpack.com!
OCaml's notion of a functor is not the one from category theory, it is a higher-order module.
So we simply settled for "module function".
Furthermore we have documented them properly now. Thank you, @vlkpack.com!