diff --git a/tortoise/.direnv/flake-profile b/tortoise/.direnv/flake-profile
index 0c05709..f9f4da1 120000
--- a/tortoise/.direnv/flake-profile
+++ b/tortoise/.direnv/flake-profile
@@ -1 +1 @@
-flake-profile-1-link
\ No newline at end of file
+flake-profile-18-link
\ No newline at end of file
diff --git a/tortoise/.direnv/flake-profile-1-link b/tortoise/.direnv/flake-profile-1-link
deleted file mode 120000
index e583a7d..0000000
--- a/tortoise/.direnv/flake-profile-1-link
+++ /dev/null
@@ -1 +0,0 @@
-/nix/store/ml5jibqk9rhd8gfps532ry58njp2j5sd-nix-shell-env
\ No newline at end of file
diff --git a/tortoise/.direnv/flake-profile-18-link b/tortoise/.direnv/flake-profile-18-link
new file mode 120000
index 0000000..60c8dcd
--- /dev/null
+++ b/tortoise/.direnv/flake-profile-18-link
@@ -0,0 +1 @@
+/nix/store/d9kjbddwp2dsiwpvdvmaff9lpgy5rhsv-nix-shell-env
\ No newline at end of file
diff --git a/tortoise/flake.nix b/tortoise/flake.nix
index 8f38de5..623929f 100644
--- a/tortoise/flake.nix
+++ b/tortoise/flake.nix
@@ -1,23 +1,37 @@
 {
-  description = "A Nix-flake-based Guile development environment";
+  description = "A Nix-flake-based C/C++ development environment";
+
   inputs.nixpkgs.url = "https://flakehub.com/f/NixOS/nixpkgs/0.1.*.tar.gz";
 
   outputs = { self, nixpkgs }:
     let
-      supportedSystems =
-        [ "x86_64-linux" ];
-      forEachSupportedSystem = f:
-        nixpkgs.lib.genAttrs supportedSystems
-        (system: f { pkgs = import nixpkgs { inherit system; }; });
-    in {
+      supportedSystems = [ "x86_64-linux" ];
+      forEachSupportedSystem = f: nixpkgs.lib.genAttrs supportedSystems (system: f {
+        pkgs = import nixpkgs { inherit system; };
+      });
+    in
+    {
       devShells = forEachSupportedSystem ({ pkgs }: {
-        default = pkgs.mkShell {
-          packages = with pkgs; [
-            gnuplot
-            guile
-            gcc
-          ];
-        };
+        default = pkgs.mkShell.override
+          {
+            # Override stdenv in order to change compiler:
+            stdenv = pkgs.clangStdenv;
+          }
+          {
+            packages = with pkgs; [
+              clang-tools
+              cmake
+              codespell
+              conan
+              cppcheck
+              doxygen
+              gtest
+              lcov
+              vcpkg
+              vcpkg-tool
+            ] ++ (if system == "aarch64-darwin" then [ ] else [ gdb ]);
+          };
       });
     };
 }
+
diff --git a/tortoise/tortoise b/tortoise/tortoise
deleted file mode 100755
index 1358568..0000000
Binary files a/tortoise/tortoise and /dev/null differ
diff --git a/tortoise/tortoise.c b/tortoise/tortoise.c
index 985a762..30e6f55 100644
--- a/tortoise/tortoise.c
+++ b/tortoise/tortoise.c
@@ -24,7 +24,7 @@ start_gnuplot() {
   if (!pid) {
     dup2 (pipes[0], STDIN_FILENO);
     execlp ("gnuplot", NULL);
-    return; /* Not reached. */
+    return 0; /* Not reached. */
   }
 
   output = fdopen(pipes[1], "w");
@@ -51,14 +51,6 @@ static void tortoise_reset () {
   fprintf(global_output, "clear\n");
   fflush(global_output);
 }
-
-
-int main(int argc, char *argv[]) {
-  global_output = start_gnuplot();
-  tortoise_reset ();
-  return EXIT_SUCCESS;
-}
-
 static void draw_line(FILE *output, double x1, double y1, double x2,
                       double y2) {
   fprintf(output, "plot [0:1] %f + %f * t, %f + %f * t notitle\n",
@@ -74,6 +66,11 @@ static void tortoise_penup() {
   pendown = 0;
 }
 
+static void tortoise_turn (double degrees)
+{
+  direction += M_PI / 180.0 * degrees;
+}
+
 static void tortoise_move(double length) {
   double newX, newY;
 
@@ -86,3 +83,17 @@ static void tortoise_move(double length) {
   x = newX;
   y = newY;
 }
+
+
+int main(int argc, char *argv[]) {
+  global_output = start_gnuplot();
+  tortoise_reset ();
+  int i;
+  tortoise_pendown();
+  for (i = 1; i <= 4; ++i) {
+    tortoise_move(3.0);
+    tortoise_turn(90.0); 
+  };
+  return EXIT_SUCCESS;
+}
+