sail

There are even more algebras on the same bits, when you take signed integers into account, such as saturating arithmetic. One interesting programming language construct that might be useful in this context are Opaque Type Synonyms, a refined form of C's typedef, which modern languages like Rust, Haskell, Go or Scala offer. This allows the programmer to use the same underlying types (e.g. int), give it different names, and define different algebras with the alias. The typing system prevents the different aliases accidentally to flow into each other. Of course that alone does not help to manage the profusion of algebras over the same bits. I think a better approach for a high-level programming language is to follow assembly and really use different names for different operations, e.g. not have + build in. Instead use explicit names like

Another way to build emulators that I am very interested in is to start from a spec, and automatically translate it into executable code. High-fidelity emulators have a lot of potential for testing and verification. The best example I know of is Sail [1]. Among other, they have RISC-V spec [2] and a bunch of compiler back-ends. They can already generate C or OCaml emulators, and I have been working on a new Rust back-end recently. [1]: https://github.com/rems-project/sail [2]: https://github.com/riscv/sail-riscv

Sail is pretty similar to ASL (both current ASL and ASL 1.0) except that (1) it has a more expressive type system, so that bitvector lengths can all be statically checked, (2) it has proper tagged unions and pattern matching, and (3) there's a wide range of open-source tooling available, for execution, specification coverage, generating emulators, integrating with relaxed concurrency models, generating theorem-prover definitions, etc. We've recently updated the Sail README, which spells some of this out: https://github.com/rems-project/sail . As Alastair Reid says, one of the main things missing in the current RISC-V specification documents is simply that the associated Sail definitions are not yet interspersed with the prose instruction descriptions. The infrastructure to do that has been available for some time, in the Sail AsciiDoc su

That's completely feasible and there are languages that do this. It doesn't really eliminate the need to run your program unless the inputs to your program are also completely restricted types like One, Two, Three. In which case yeah, you don't need to run it and the type system can just tell you the answer. I believe you can do that sort of thing in loads of type systems, e.g. Typescript, but there are languages that intentionally support it. I use a niche DSL that has fancy types like this called Sail. https://github.com/rems-project/sail In my experience the downsides of these fancy "first class type systems" are 1. More incomprehensible error messages. 2. The type checker moves from a deterministic process that either succeeds or fails in an understandable way, to SMT solvers which can just say "yep it's ok" or "nope, couldn't prove i