change lean version error??

Author: Atticus Kuhn

README.md

@@ -11,3 +11,16 @@ To set up your new GitHub repository, follow these steps:
 * In the **Source** dropdown menu, select "GitHub Actions".
 
 After following the steps above, you can remove this section from the README file.
+
+## Development
+
+- Enter the dev shell with `nix develop`. The shell uses `elan` to provide the
+  Lean toolchain specified in `lean-toolchain` (currently `leanprover/lean4:v4.24.0`).
+  The flake does not pin a Lean version via nix overlays to avoid version skew.
+
+- First time in the shell, `elan` will install the requested toolchain. Then:
+  - Check the compiler: `lean --version` should report `4.24.0`.
+  - Build the project: `lake build`.
+
+If you prefer not to use the dev shell, you can install `elan` separately and run
+`elan toolchain install $(cat lean-toolchain)` to provision Lean + Lake, then `lake build`.

docs/techContext.md

@@ -7,6 +7,13 @@ Stack:
 - Dependencies: `Std` (TreeMap), `Mathlib` (lexicographic ordering helpers).
 - Rust toolchain (`rustc` and `cargo`) available in dev/CI environments.
 
+Dev environment:
+
+- Enter with `nix develop`. The shell uses `elan` to install and expose the
+  Lean/Lake toolchain specified in `lean-toolchain` (currently `leanprover/lean4:v4.24.0`).
+  We avoid pinning Lean via a Nix overlay to prevent version skew with Mathlib; the
+  shell prepends the matching `elan` toolchain `bin` directory to `PATH`.
+
 Key modules:
 
 - `PartIiProject/Term.lean`: core types, semimodule evidence, tensor, PHOAS terms, interpreter, printers, examples.

flake.nix

@@ -4,13 +4,18 @@
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
     flake-parts.url = "github:hercules-ci/flake-parts";
+    # Keep lean4-nix as an input in case we restore Nix builds later,
+    # but do not depend on its toolchain overlay for dev shells.
     lean4-nix.url = "github:lenianiva/lean4-nix";
   };
 
   outputs = inputs @ {
     nixpkgs,
     flake-parts,
     lean4-nix,
+    # lean4-nix is intentionally unused in devShell to avoid pinning Lean
+    # in Nix. We rely on `elan` + `lean-toolchain` instead.
+    # It remains available in `inputs` for future use.
     ...
   }:
     flake-parts.lib.mkFlake { inherit inputs; } {
@@ -23,44 +28,35 @@
 
       perSystem = { system, ... }:
         let
-          pkgs = import nixpkgs {
-            inherit system;
-            overlays = [ (lean4-nix.readToolchainFile ./lean-toolchain) ];
-          };
-          lake = (lean4-nix.lake { inherit pkgs; });
-          # Build the test executable via lake-manifest integration
-          sdqlTests = (lake.mkPackage {
-            src = ./.;
-            # Explicit roots to avoid auto-capitalization from manifest name
-            roots = [ "Tests" ];
-          }).executable;
+          # Use plain nixpkgs for the dev shell; do not pin Lean here.
+          # Lean/Lake will come from `elan` according to `lean-toolchain`.
+          pkgs = import nixpkgs { inherit system; };
         in
         {
-          packages = {
-            default = sdqlTests;
-            sdql-tests = sdqlTests;
-          };
-
-          # The executable name defaults to the lowercased manifest name
-          # (see lean4-nix buildLeanPackage), which for this repo is
-          # "part_ii_project".
-          apps = let exePath = "${sdqlTests}/bin/part_ii_project"; in {
-            default = {
-              type = "app";
-              program = exePath;
-            };
-            sdql-tests = {
-              type = "app";
-              program = exePath;
-            };
-          };
-
           devShells.default = pkgs.mkShell {
-            # Provide Lean + Lake matching ./lean-toolchain, plus essential tools.
-            # Keep this minimal to avoid attr or non-derivation issues on some channels.
-            packages =
-              (with pkgs.lean; [ lean-all ])
-              ++ (with pkgs; [ git unzip rustc cargo codex uv ]);
+            # Keep the shell minimal and reproducible. We rely on `elan`
+            # to supply Lean/Lake that match `./lean-toolchain`.
+            packages = with pkgs; [ git unzip rustc cargo codex uv elan ];
+
+            # Ensure the desired toolchain is available and preferred.
+            # This avoids depending on a Lean version packaged in nixpkgs
+            # or an overlay that may lag behind the toolchain file.
+            shellHook = ''
+              if command -v elan >/dev/null 2>&1; then
+                TOOLCHAIN=$(cat lean-toolchain)
+                echo "Using Lean toolchain $TOOLCHAIN via elan"
+                # Try to install silently if missing (ignore failures offline)
+                elan toolchain install "$TOOLCHAIN" >/dev/null 2>&1 || true
+                # Derive the toolchain path used by elan without shell parameter expansion
+                ELAN_TC=$(printf "%s" "$TOOLCHAIN" | sed -e 's#/#--#g' -e 's#:#---#g')
+                ELAN_BIN="$HOME/.elan/toolchains/$ELAN_TC/bin"
+                if [ -d "$ELAN_BIN" ]; then
+                  export PATH="$ELAN_BIN:$PATH"
+                fi
+              else
+                echo "Warning: elan not found; system Lean/Lake (if any) will be used."
+              fi
+            '';
           };
         };
     };

lean-toolchain

@@ -1 +1 @@
-leanprover/lean4:v4.23.0
+leanprover/lean4:v4.24.0