letlang VS dafny

That works for any types (except the functional types), and even the generic ones. During code generation, I create structs that implement the Type trait.

As stated on the website ( https://letlang.dev ), Letlang is a general-purpose language.

Author here, the article is more about how Rust and its ecosystem are nice tools for language designers rather than the beauty of Lisp.

The crates listed in that article are the ones I use for my compiler: https://letlang.dev

Lisp was only chosen as a way to demonstrate the power of those crates and Rust features. A kind of way of justifying my choices for Letlang.

It's not "you should do it like this" but "you can do it like this".

"Faster than C", I saw people write C code slower than a Python equivalent. So I have to admit, I don't know what it means for a language to be fast, because it depends on the algorithm being implemented.

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"simpler than Python", what does "simple" mean?

Simple design? Python's design is very complex (take a look at "Crimes with Python's pattern matching" < https://www.hillelwayne.com/post/python-abc/ > for example), on the other hand, assembly languages, or Lisp, or Forth, have a very simple design.

Simple as in "easy to use"? Rust is easy, write code, fix what the compiler tells you you did wrong. Joke aside, Go is quite easy to use and while I personally don't like this language, I get why it replaced Python in a lot of use cases.

Also, once you get used to the OTP framework, Erlang/Elixir/Gleam/any beam language are quite easy to use and have less footguns than Python.

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"safer than Rust" is too vague. Is it memory safety? type safety? thread safety? cosmic ray safety? A mix of all of that?

Let's guess you meant "memory safety". All languages with a Garbage Collector are "memory safe".

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On a semi-unrelated note, I've been working on https://letlang.dev

It's a language inspired by Erlang/Elixir (same concurrency model) that compiles to Rust code (the runtime use tokio). It is immutable, have no Garbage Collector thanks to Rust semantics, and dynamically typed.

I haven't run any benchmark (it's not even finished, I've been working on the specification before continuing the implementation), but I guess it could be slower than a rock.

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For some recommendations, have you looked at Zig? Nim? Hare?

  https://ziglang.org/

In my language (Letlang), I use the keyword class with structural pattern matching and optionally a predicate. Types (or rather, classes) can be combined with logical operators &, |, !:

Not sure this is what GP is talking about but to implement the actor model in https://letlang.dev I use tokio.

In the early drafts of Letlang, I had the goal to add an equation solver. I got rid of that because:

I'm working on a programming language inspired by erlang and which compiles to Rust: https://letlang.dev

For a contract based language and a "really dynamically typed language", I'm working on https://letlang.dev

And it's because I haven't thought yet about how to do static type checking with such a feature.

I haven't got any time to work on it in the past few weeks, and I'm the only dev (would really love some help). So, it will be ready when it will be ready :P

I use Rust generators to implement them, a rudimentary example: https://github.com/linkdd/letlang/blob/main/letlang_runtime/src/utils/entrypoint.rs

For those that are interested but perhaps not aware in this similar project, Dafny is a "verification-aware programming language" that can compile to rust: https://github.com/dafny-lang/dafny

Code correctness is a lost art. I requirement to think in abstractions is what scares a lot of devs to avoid it. The higher abstraction language (formal specs) focus on a dedicated language to describe code, whereas lower abstractions (code contracts) basically replace validation logic with a better model.

C# once had Code Contracts[1]; a simple yet powerful way to make formal specifications. The contracts was checked at compile time using the Z3 SMT solver[2]. It was unfortunately deprecated after a few years[3] and once removed from the .NET Runtime it was declared dead.

The closest thing C# now have is probably Dafny[4] while the C# dev guys still try to figure out how to implement it directly in the language[5].

[1] https://www.microsoft.com/en-us/research/project/code-contra...

[2] https://github.com/Z3Prover/z3

[3] https://github.com/microsoft/CodeContracts

[4] https://github.com/dafny-lang/dafny

[5] https://github.com/dotnet/csharplang/issues/105

I don't think something that specific exists. There are a very large number of formal methods tools, each with different specialties / domains.

For verification with proof assistants, [Software Foundations](https://softwarefoundations.cis.upenn.edu/) and [Concrete Semantics](http://concrete-semantics.org/) are both solid.

For verification via model checking, you can check out [Learn TLA+](https://learntla.com/), and the more theoretical [Specifying Systems](https://lamport.azurewebsites.net/tla/book-02-08-08.pdf).

For more theory, check out [Formal Reasoning About Programs](http://adam.chlipala.net/frap/).

And for general projects look at [F*](https://www.fstar-lang.org/) and [Dafny](https://dafny.org/).

Dafny and Whiley are two examples with explicit verification support. Idris and other dependently typed languages should all be rich enough to express the required predicate but might not necessarily be able to accept a reasonable implementation as proof. Isabelle, Lean, Coq, and other theorem provers definitely can express the capability but aren't going to churn out much in the way of executable programs; they're more useful to guide an implementation in a more practical functional language but then the proof is separated from the implementation, and you could also use tools like TLA+.

https://dafny.org/

https://whiley.org/

https://www.idris-lang.org/

https://isabelle.in.tum.de/

https://leanprover.github.io/

https://coq.inria.fr/

http://lamport.azurewebsites.net/tla/tla.html

> I think we can assume it won't be as efficient has hand written code

Actually, surprisingly, not necessarily the case!

If you'll refer to the discussion in https://github.com/dafny-lang/dafny/issues/601 and in https://github.com/dafny-lang/dafny/issues/547, Dafny can statically prove that certain compiler branches are not possible and will never be taken (such as out-of-bounds on index access, logical assumptions about whether a value is greater than or less than some other value, etc). This lets you code in the assumptions (__assume in C++ or unreachable_unchecked() under rust) that will allow the compiler to optimize the codegen using this information.