nix flake/direnv

.envrc

@@ -0,0 +1 @@
+use flake

flake.lock

@@ -0,0 +1,96 @@
+{
+  "nodes": {
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1731533236,
+        "narHash": "sha256-l0KFg5HjrsfsO/JpG+r7fRrqm12kzFHyUHqHCVpMMbI=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "11707dc2f618dd54ca8739b309ec4fc024de578b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1753939845,
+        "narHash": "sha256-K2ViRJfdVGE8tpJejs8Qpvvejks1+A4GQej/lBk5y7I=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "94def634a20494ee057c76998843c015909d6311",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs_2": {
+      "locked": {
+        "lastModified": 1744536153,
+        "narHash": "sha256-awS2zRgF4uTwrOKwwiJcByDzDOdo3Q1rPZbiHQg/N38=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "18dd725c29603f582cf1900e0d25f9f1063dbf11",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs",
+        "rust-overlays": "rust-overlays"
+      }
+    },
+    "rust-overlays": {
+      "inputs": {
+        "nixpkgs": "nixpkgs_2"
+      },
+      "locked": {
+        "lastModified": 1754102567,
+        "narHash": "sha256-d6nZ+1e4VDqW6VAwfx9EAUDJdPxSwqwGiuli32FEgoE=",
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "rev": "08ff39bf869cadca3102b39824f4c7025186b7dc",
+        "type": "github"
+      },
+      "original": {
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "type": "github"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,31 @@
+{
+  description = "A nix flake for nightly rust";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    rust-overlays.url = "github:oxalica/rust-overlay";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils, rust-overlays, ...}: 
+    flake-utils.lib.eachDefaultSystem (system: let
+      overlays = [
+        (import rust-overlays)
+      ];
+      pkgs = import nixpkgs {
+        inherit system overlays;
+      };
+      rust = pkgs.rust-bin.selectLatestNightlyWith (toolchain: toolchain.default.override {
+        extensions = ["rust-src" "rust-analyzer"];
+        targets = [ "x86_64-unknown-linux-gnu" ];
+      });
+    in with pkgs; {
+      devShells.default = pkgs.mkShell {
+        buildInputs = [
+          pkg-config
+          git
+          rust
+        ];
+      };
+    });
+}

src/ast2/biunification.rs

@@ -0,0 +1,88 @@
+//! Type checking for the AST.
+//! This module implements a bi-unification type-checking algorithm to infer
+//! types for each node in the AST.
+
+// Visitor pattern has lots of unused arguments
+#![allow(unused_variables)]
+
+use std::collections::HashMap;
+
+use super::{Ast, Index, intern, visitor::AstVisitorTrait};
+
+type Id = u32;
+
+enum Type {
+    Reified(intern::Index),
+    Variable(Id),
+}
+
+/// Variance of a type parameter or constraint.
+/// A function of type `A -> B` is covariant in `B` and contravariant in `A`.
+/// This means that a type `T` may be substituted for `A` if `T` is a subtype of `A`, but
+/// a type `T` may only be substituted for `B` if `T` is a supertype of `B`.
+///
+/// Namely, in a type system with `int` and `nat <: int`, for a function `f: int
+/// -> int` in the expression `let u: int = 3; let t: nat = f(u);`, `u` may
+/// safely be used as an argument to `f` because `nat <: int`, but `f(u`)` may
+/// not be assigned to `t` because `int <: nat` is not true.
+enum Variance {
+    #[doc(alias = "Positive")]
+    Covariant,
+    #[doc(alias = "Negative")]
+    Contravariant,
+}
+
+#[derive(Debug, Clone, Copy)]
+struct Value(Id);
+#[derive(Debug, Clone, Copy)]
+struct Use(Id);
+
+/// Typechecking error.
+#[derive(Debug, Clone, thiserror::Error)]
+enum Error {
+    #[error("Unimplemented feature")]
+    Unimplemented,
+}
+
+type Result<T> = std::result::Result<T, Error>;
+
+struct Bindings {
+    inner: HashMap<super::Index, Value>,
+}
+
+struct TypeChecker<'a> {
+    pool: &'a mut intern::InternPool,
+}
+
+// Core
+impl TypeChecker<'_> {
+    pub fn new(pool: &mut intern::InternPool) -> TypeChecker {
+        TypeChecker { pool }
+    }
+
+    fn var(&mut self) -> (Value, Use) {
+        todo!()
+    }
+}
+
+// Frontend
+
+impl<'a> AstVisitorTrait<&'a Ast> for TypeChecker<'_> {
+    type Error = Error;
+    type Value = Value;
+
+    const UNIMPL: Self::Error = Error::Unimplemented;
+
+    fn visit_constant_impl(
+        &mut self,
+        ast: &'a Ast,
+        idx: Index,
+        ty: Index,
+        value: intern::Index,
+    ) -> std::result::Result<Self::Value, Self::Error> {
+        // constants may be of type `comptime_int`, which is a special type that
+        // cannot exist at runtime.
+
+        todo!()
+    }
+}

src/ast2/mod.rs

@@ -13,6 +13,7 @@ use crate::{
     symbol_table::syms2::DeclKind, tokens::Token,
 };
 
+pub mod biunification;
 pub mod debug;
 pub mod intern;
 pub mod ir;
@@ -586,6 +587,7 @@ mod index {
         }
     }
 
+    /// Index tyoe for the AST.
     /// Index type that has 28 bits of index and 4 bits of kind.
     #[repr(transparent)]
     #[derive(Clone, Copy, Hash, PartialEq, Eq, PartialOrd, Ord)]

src/ast2/typecheck.rs

@@ -1,7 +1,3 @@
-//! Type checking for the AST.
-//! This module implements a bi-unification type-checking algorithm to infer
-//! types for each node in the AST.
-
 // Visitor pattern has lots of unused arguments
 #![allow(unused_variables)]