Mantis

Mantis is my attempt at the language I want to write: Rust’s safety without making every program pay the full cost of proving it. The plan is borrow checking by default, with an escape hatch the compiler can take for you: it decides per variable whether a value should be owned, reference-counted or garbage-collected, and lifetimes are more implicit than in Rust.

It’s an ambitious goal and it’s far from done. What exists today is a real compiler that produces native binaries, a standard library written in Mantis, and the tooling to edit it comfortably.

type MyEnum = enum {
  None,
  MyStruct(MyStruct),
}

fn main() {
  let my_enum = MyEnum.MyStruct(String.fromStr("Hello World"));

  if MyEnum.MyStruct(ms) = my_enum {
    println(ms.as_str());
  }
}

The compiler

The pipeline is split into crates, so each stage can be tested and reused on its own:

Code generation goes through Cranelift, the backend behind Wasmtime. The same IR becomes an object file to link into a native binary, or is JIT-compiled and run straight away.

  source -> lexer -> parser -> checks -> codegen -> binary
                                 |
                       unsafe programs stop here

Figure 1: Compiler pipeline

The language so far

• Structs, enums and generics, with impl blocks and pattern matching: Option[T] and Result in the standard library are written in Mantis itself.
• Pointers and lambdas, with a test suite of small programs covering control flow, generics, nested structs and pointers.
• C interop. Functions marked extern bind straight to libc. One example is an HTTP file server built on raw socket, bind, listen and accept calls.
• A multithreaded async runtime, written in Mantis, that spawns tasks across worker threads and blocks until they finish.
• A standard library covering strings, vectors, files, I/O, environment access and TOML parsing.

Tooling

A language nobody can edit doesn’t get used, even by its author. Mantis ships a Tree-sitter grammar with highlight, indent and text-object queries, and a one-command script that builds the grammar, validates every query against real code and installs both it and the language server into the Helix editor.