4 ms·

The Lisp in the Cellar: Dependent types that live upstairs [pdf]

88 points by todsacerdoti 1y ago

Downloadable: https://zenodo.org/records/15424968/files/deputy-els.pdf https://zenodo.org/records/15424968/files/deputy-els.pdf

TacticalCoder 1y ago
[flagged]
- deleted 1y ago
  [deleted]
droideqa 1y ago
Sadly "deputy clojure" on Google brings no results... The only hint is this repo[0] referenced in the paper. [0]: https://gitlab.com/fredokun/deputy https://gitlab.com/fredokun/deputy
- agumonkey 1y ago
  Pretty readable code
reuben364 1y ago
Thinking out aloud here. One pattern that I have frequently used in EMACS elisp is that redefining a top-level value overwrites that value rather than shadowing it. Basically hot reloading. This doesn't work in a dependently typed context as the type of subsequent definitions can depend on values of earlier definitions. def t := string def x: t := "asdf" redef t := int redefining t here would cause x to fail to type check. So the only options are to either shadow the variable t, or have redefinitions type-check all terms whose types depend on the value being redefined. Excluding the type-level debugging they mention, I think a lean style language-server is a better approach. Otherwise you are basically using an append-only ed to edit your environment rather than a vi.
- extrabajs 1y ago
  I don’t see the connection to dependent types. But anyway, is ‘redef’ part of your language? What type would you give it?
  - reuben364 1y ago
    I just wrote redef to emphasize that I'm not shadowing the original definition. def a := 1 def f x := a * x -- at this point f 1 evaluates to 1 redef a := 2 -- at this point f 1 evaluates to 2 But with dependent types, types can depend on prior values (in the previous example the type of x depends on the value t in the most direct way possible, as the type of x is t). If you redefine values, the subsequent definitions may not type-check anymore.
    - extrabajs 1y ago
      I see what you mean. But would you not experience the same sort of issue simply from redefining types in the same way? It seems this kind of destructive operation (whether on types or terms) is the issue. As someone who's used to ML, it seems strange to allow this kind of thing (instead of simply shadowing), but maybe it's a Lisp thing?
- resize2996 1y ago
  > EMACS elisp I used this to write the front end for an ATM machine.
- wk_end 1y ago
  I've fantasized about some kind of a dependently-typed Smalltalk-like thing before, and in those fantasies the solution would be that changes would be submitted in the form of transactions - they wouldn't be live until you bundled them all together into one big change that would be fully type-checked, as you describe.
- kscarlet 1y ago
  The only option that you described is called "hyperstatic global environment". And it is called that for a reason, it is not very dynamic :) and probably too static to the taste of many Lisp and all Smalltalk fans.
dang 1y ago
Any URL for this that we can open in a browser (as opposed to the dreaded "Content-Disposition: attachment")?
- Jtsummers 1y ago
  https://zenodo.org/records/15424968 https://zenodo.org/records/15424968 - This at least takes you to a webpage where you can view the paper. If you select to download it, it still downloads of course instead of just opening in the browser.
  - dang 1y ago
    Thanks! I've switched to that above, and put the downloadable link in the top text.
reikonomusha 1y ago
Related context: The 2025 European Lisp Symposium [1] was just wrapped a few hours ago in Zurich. There was content on: - Static typing a la Haskell with Coalton in Common Lisp - Dependent typing with Deputy in Clojure (this post) - The Common Lisp compiler SBCL ported to the Nintendo Switch - Common Lisp and AI/deep learning - A special retrospective on Modula and Oberon - Many lightning talks. [1] https://european-lisp-symposium.org/2025/index.html https://european-lisp-symposium.org/2025/index.html
- deleted 1y ago
  [deleted]
- no_wizard 1y ago
  I feel like Lisp would be an ideal language for AI development. Its exceedingly good for DSL development and pattern matching. Its already structurally like math notation as well, which I would think would lend itself to thinking how models would consume information and learn
  - rscho 1y ago
    Well... believe it or not, some have thought of using lisp for AI for quite some time. ;-)
  - froh 1y ago
    indeed. Peter Norvig, 1992 Paradigms of AI Programming: Case Studies in Common Lisp https://g.co/kgs/hck8wsE https://g.co/kgs/hck8wsE https://en.m.wikipedia.org/wiki/Peter_Norvig https://en.m.wikipedia.org/wiki/Peter_Norvig it's no coincidence Google is actively maintaining sbcl, either.
    - Zambyte 1y ago
      Why not go all the way to the source? John McCarthy coined the term "artificial intelligence", and then invented / discovered LISP in pursuit of it in the 1950s :D
  - ayrtondesozzla 1y ago
fithisux 1y ago
Impressive.
sfpityparty 1y ago
[flagged]

88 points by todsacerdoti 1y ago

Downloadable: https://zenodo.org/records/15424968/files/deputy-els.pdf https://zenodo.org/records/15424968/files/deputy-els.pdf

TacticalCoder 1y ago

[flagged]

deleted 1y ago
[deleted]

droideqa 1y ago

Sadly "deputy clojure" on Google brings no results... The only hint is this repo[0] referenced in the paper. [0]: https://gitlab.com/fredokun/deputy https://gitlab.com/fredokun/deputy

agumonkey 1y ago
Pretty readable code

reuben364 1y ago

Thinking out aloud here. One pattern that I have frequently used in EMACS elisp is that redefining a top-level value overwrites that value rather than shadowing it. Basically hot reloading. This doesn't work in a dependently typed context as the type of subsequent definitions can depend on values of earlier definitions. def t := string def x: t := "asdf" redef t := int redefining t here would cause x to fail to type check. So the only options are to either shadow the variable t, or have redefinitions type-check all terms whose types depend on the value being redefined. Excluding the type-level debugging they mention, I think a lean style language-server is a better approach. Otherwise you are basically using an append-only ed to edit your environment rather than a vi.

extrabajs 1y ago
I don’t see the connection to dependent types. But anyway, is ‘redef’ part of your language? What type would you give it?
- reuben364 1y ago
  I just wrote redef to emphasize that I'm not shadowing the original definition. def a := 1 def f x := a * x -- at this point f 1 evaluates to 1 redef a := 2 -- at this point f 1 evaluates to 2 But with dependent types, types can depend on prior values (in the previous example the type of x depends on the value t in the most direct way possible, as the type of x is t). If you redefine values, the subsequent definitions may not type-check anymore.
  - extrabajs 1y ago
    I see what you mean. But would you not experience the same sort of issue simply from redefining types in the same way? It seems this kind of destructive operation (whether on types or terms) is the issue. As someone who's used to ML, it seems strange to allow this kind of thing (instead of simply shadowing), but maybe it's a Lisp thing?
resize2996 1y ago
> EMACS elisp I used this to write the front end for an ATM machine.
wk_end 1y ago
I've fantasized about some kind of a dependently-typed Smalltalk-like thing before, and in those fantasies the solution would be that changes would be submitted in the form of transactions - they wouldn't be live until you bundled them all together into one big change that would be fully type-checked, as you describe.
kscarlet 1y ago
The only option that you described is called "hyperstatic global environment". And it is called that for a reason, it is not very dynamic :) and probably too static to the taste of many Lisp and all Smalltalk fans.

dang 1y ago

Any URL for this that we can open in a browser (as opposed to the dreaded "Content-Disposition: attachment")?

Jtsummers 1y ago
https://zenodo.org/records/15424968 https://zenodo.org/records/15424968 - This at least takes you to a webpage where you can view the paper. If you select to download it, it still downloads of course instead of just opening in the browser.
- dang 1y ago
  Thanks! I've switched to that above, and put the downloadable link in the top text.

reikonomusha 1y ago

Related context: The 2025 European Lisp Symposium [1] was just wrapped a few hours ago in Zurich. There was content on: - Static typing a la Haskell with Coalton in Common Lisp - Dependent typing with Deputy in Clojure (this post) - The Common Lisp compiler SBCL ported to the Nintendo Switch - Common Lisp and AI/deep learning - A special retrospective on Modula and Oberon - Many lightning talks. [1] https://european-lisp-symposium.org/2025/index.html https://european-lisp-symposium.org/2025/index.html

deleted 1y ago
[deleted]
no_wizard 1y ago
I feel like Lisp would be an ideal language for AI development. Its exceedingly good for DSL development and pattern matching. Its already structurally like math notation as well, which I would think would lend itself to thinking how models would consume information and learn
- rscho 1y ago
  Well... believe it or not, some have thought of using lisp for AI for quite some time. ;-)
- froh 1y ago
  indeed. Peter Norvig, 1992 Paradigms of AI Programming: Case Studies in Common Lisp https://g.co/kgs/hck8wsE https://g.co/kgs/hck8wsE https://en.m.wikipedia.org/wiki/Peter_Norvig https://en.m.wikipedia.org/wiki/Peter_Norvig it's no coincidence Google is actively maintaining sbcl, either.
  - Zambyte 1y ago
    Why not go all the way to the source? John McCarthy coined the term "artificial intelligence", and then invented / discovered LISP in pursuit of it in the 1950s :D
- ayrtondesozzla 1y ago

fithisux 1y ago

Impressive.

sfpityparty 1y ago

[flagged]