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What about Lisps then? They don't have the type system but you probably win on verbosity. I thought that Racket and other Lisps have some static typing/ADT support too, but I'm not familiar with them.

I first heard the term "nanopass" from this paper [1], which is done in Scheme:

https://scholar.google.com/scholar?cluster=18108599075280184...

[1] Sarkar, Dipanwita, Oscar Waddell, and R. Kent Dybvig. "A Nanopass Framework for Compiler Education."



> What about Lisps then?

That's what I'm using at the moment, but I'm really missing the strict typing. It's often hard to debug even the simple passes if they're constructing invalid trees. A type system would have picked it up easily.

For this reason I'm working on a hybrid DSL which combines all the power of a Nanopass-like visitors language and a Hindley-Milner type inference with a little twist to overcome the expression problem. Plus all the bells and whistles like an enforced totality, combined with locally allowed imperative things (updating hash maps, accumulating data destructively in lists, etc.).


This article covers setting up Common Lisp with GADTs and exhaustive pattern-matching checks. https://chriskohlhepp.wordpress.com/metacircular-adventures-...

> We note that we get a non-exhaustive match warning at compile time, not run time. This is the behaviour we would expect for example from OCaml. Indeed, in our little game we might change the simple use of keyword symbols to algebraic data types and thus add compiler hosted verification of our pattern matches. To bring our exploration of the meta-circular abstraction to a full circle: Abstract data-types are an ideal medium in which to represent Abstract Syntax Trees or ASTs. Indeed the whole of Lisp syntax is itself fundamentally an Abstract Syntax Tree. So let’s see if we can represent trees using the cl-algebraic-datatype package. That would amount to an Abstract Syntax Tree represented inside an Abstract Syntax Tree. We will close with that that little teaser.


Is the DSL embedded in a Lisp or is it an entirely new language? Isn't there a lot of existing work on type systems and ADTs in Lisps? e.g.

http://docs.racket-lang.org/ts-guide/types.html#%28part._.Un...

https://www.reddit.com/r/lisp/comments/16vwib/which_lisps_fe...

I ask because I have run into the typing problem writing language tools in Python, and then I switched to OCaml. I am not that experienced with it, but I see the problem you're talking about. I'm wondering if I should go to a Lisp. Racket looks interesting and this seems like something the community cares about.


Yes, it is a eDSL on top of Lisp (but I also have a proper ML which runs on top of Lisp, so it does not matter much).

The issue with the existing type systems is that they do not solve the expression problem, for this reason I had to build a new one from scratch.

I'd suggest taking a look at Nanopass (there is a Racket port). I doubt it will play well with any external type systems, but at least some of the ideas in it are very valuable.


I proposed integrating FLINT ML compiler and VLISP in some form for heightened correctness argument, ML safety, and LISP power. Kind of several copies of the software that corresponded with the strengths of each catching various problems and assuring correctness of tool itself.

Never occurred to me to embed ML in LISP. Looks so obvious in hindsight. You might be onto something there. Integrating yours with mine, if I get back to using those, might embed CakeML or Ocaml subset in VLISP with it emulated in Racket or CL knockoff of it for fast, day-to-day development.

Btw, what's the expression problem? I've either forgotten or not got that deep into PL design yet.


Originally ML was implemented in Lisp. It was the language for a theorem prover: HOL

https://en.wikipedia.org/wiki/HOL_(proof_assistant)

Older ML (not something like SML) in Lisp is still available in some old version of that prover.


Interesting. So, basically taking it full-circle back where it came from. That is, if one still uses it with HOL4 for verification.


The term was coined by Philip Wadler: https://en.wikipedia.org/wiki/Expression_problem

The older versions of Bigloo used to contain an ML compiler built on top of Scheme (they dropped it later for some reason), so the concept is not new.


Appreciate the reference. Will look into it in the future. The Wikipedia summary made sense but the recompile part doesnt bother me as much as others. My preferrence is to make compiles fast as possible with good incremental compilation and caching. Ive even pushed for trying to FPGA-accelerate compiler passes if possible.


My solution allows incremental compilation. It is just a type system hack, and it does not even involve backtracking (my second favourite compilation technique), just a two pass typing instead of a single pass.

As for the compilation speed, the Nanpass-like approach is very parallelisable and there is a lot of space for nice optimisations (like pass fusion).


Curious, do you publish your tools that implement your solution?


Only partially (see the discussion elsewhere in this thread). It's a work in progress. But I hope to be able to roll out a working prototype soon.

The main component of this type system (weak sets unification) is already published.


Cool, cool.


IIRC, you are into both tech like ML and hardware. I know of LISP machines & even a G-machine (Haskell) emulator on a Forth chip. However, given verification and non-Turing push, I was looking for a CPU to run algorithms written in Standard ML. Found one and thought you'd enjoy reading it too:

http://cstein.kings.cam.ac.uk/~chris/part2/eb379.pdf


Thanks! An interesting one. It's unusual to see an SKI-based implementation of an eager language.




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