diff --git a/.github/workflows/main-stock-ubuntu.yml b/.github/workflows/main-stock-ubuntu.yml
index 4516ac3b..dcecd246 100644
--- a/.github/workflows/main-stock-ubuntu.yml
+++ b/.github/workflows/main-stock-ubuntu.yml
@@ -107,6 +107,11 @@ jobs:
           echo "::group::xo-expression build"
           cmake --build .build -- xo-expression
 
+          echo "::group::xo-pyexpression build"
+          cmake --build .build -- xo-pyexpression
+
+          ##############
+
           echo "::group::xo build (catch all)"
           cmake --build .build #--verbose
 
diff --git a/CMakeLists.txt b/CMakeLists.txt
index dca4d8de..55119a3d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -78,8 +78,9 @@ add_subdirectory(xo-pyreflect)
 add_subdirectory(xo-ratio)
 add_subdirectory(xo-unit)
 add_subdirectory(xo-pyunit)
+#
 add_subdirectory(xo-expression)
-#add_subdirectory(xo-pyexpression)
+add_subdirectory(xo-pyexpression)
 #add_subdirectory(xo-tokenizer)
 #add_subdirectory(xo-reader)
 #add_subdirectory(xo-jit)
diff --git a/pkgs/xo-pyexpression.nix b/pkgs/xo-pyexpression.nix
new file mode 100644
index 00000000..80f9b6e6
--- /dev/null
+++ b/pkgs/xo-pyexpression.nix
@@ -0,0 +1,37 @@
+{
+  # nixpkgs dependencies
+  stdenv, cmake, catch2, # ... other deps here
+
+  # xo dependencies
+  xo-cmake, xo-pyutil, xo-expression, xo-pyreflect,
+
+  # args
+
+  #   attrset for fetching source code.
+  #    { type, owner, repo, ref }
+  #
+  #   e.g. type="github", owner="rconybea", repo="cmake-examples", ref="ex1b"
+  #
+  #   see [[../flake.nix]]
+  #
+  #cmake-examples-ex1-path
+
+  # someconfigurationoption ? false
+} :
+
+stdenv.mkDerivation (finalattrs:
+  {
+    name = "xo-pyexpression";
+    version = "1.0";
+
+    src = ../xo-pyexpression;
+
+    cmakeFlags = ["-DCMAKE_MODULE_PATH=${xo-cmake}/share/cmake"];
+    doCheck = true;
+    nativeBuildInputs = [ cmake catch2 xo-cmake ];
+    propagatedBuildInputs = [
+      xo-pyutil
+      xo-pyreflect
+      xo-expression
+    ];
+  })
diff --git a/pkgs/xo-userenv.nix b/pkgs/xo-userenv.nix
index 60782bf8..bdddd92c 100644
--- a/pkgs/xo-userenv.nix
+++ b/pkgs/xo-userenv.nix
@@ -49,7 +49,8 @@
 #  xo-pykalmanfilter, xo-websock, xo-pywebsock, xo-tokenizer,
 
   xo-expression,
-  #xo-pyexpression, xo-reader,
+  xo-pyexpression,
+# xo-reader,
 #  xo-jit,
 #  xo-pyjit
 
@@ -76,7 +77,7 @@ buildEnv {
             xo-pyunit
 
             xo-expression
-#            xo-pyexpression
+            xo-pyexpression
 #            xo-tokenizer
 #            xo-reader
 #            xo-jit