diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 4ccc0a1d7..195e8c39e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -164,6 +164,11 @@ jobs:
           cd main
           just ${{ env.JUST_ARGS }} build runtime
 
+      - name: Test Rust runtime
+        run: |
+          cd main/runtime/rust
+          cargo test --release
+
       # We use the options:
       #   - -fhide-source-paths
       #   - -fwrite-ide-info -hiedir=.hie
diff --git a/.gitignore b/.gitignore
index 8e0864e04..79e5f565b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -56,7 +56,7 @@ TAGS
 # other
 .DS_Store
 
-/runtime/include/
+/runtime/c/include/
 _build/
 _build.*/
 *.agdai
diff --git a/Makefile b/Makefile
index 924813052..4912bdfd5 100644
--- a/Makefile
+++ b/Makefile
@@ -211,7 +211,7 @@ fast-build: submodules runtime
 
 .PHONY: runtime
 runtime:
-	cd runtime && make -j 4 -s
+	cd runtime && make
 
 # -- Install
 
diff --git a/app/Commands/Compile/Native/Options.hs b/app/Commands/Compile/Native/Options.hs
index 8bdb36e62..00cc37e57 100644
--- a/app/Commands/Compile/Native/Options.hs
+++ b/app/Commands/Compile/Native/Options.hs
@@ -52,10 +52,10 @@ nativeHelperOptions opts =
           | otherwise = nativeReleaseRuntime
           where
             nativeReleaseRuntime :: BS.ByteString
-            nativeReleaseRuntime = $(FE.makeRelativeToProject "runtime/_build.native64/libjuvix.a" >>= FE.embedFile)
+            nativeReleaseRuntime = $(FE.makeRelativeToProject "runtime/c/_build.native64/libjuvix.a" >>= FE.embedFile)
 
             nativeDebugRuntime :: BS.ByteString
-            nativeDebugRuntime = $(FE.makeRelativeToProject "runtime/_build.native64-debug/libjuvix.a" >>= FE.embedFile)
+            nativeDebugRuntime = $(FE.makeRelativeToProject "runtime/c/_build.native64-debug/libjuvix.a" >>= FE.embedFile)
 
     nativeDefaultOutputFile :: Path Abs File -> Path Abs File -> Path Abs File
     nativeDefaultOutputFile inputFile baseOutputFile =
diff --git a/app/Commands/Compile/NativeWasiHelper/RuntimeWriter.hs b/app/Commands/Compile/NativeWasiHelper/RuntimeWriter.hs
index f794670c7..558dbda9e 100644
--- a/app/Commands/Compile/NativeWasiHelper/RuntimeWriter.hs
+++ b/app/Commands/Compile/NativeWasiHelper/RuntimeWriter.hs
@@ -29,4 +29,4 @@ writeRuntime runtime = do
   mapM_ (uncurry writeHeader) headersDir
   where
     headersDir :: [(Path Rel File, BS.ByteString)]
-    headersDir = map (first relFile) $(FE.makeRelativeToProject "runtime/include" >>= FE.embedDir)
+    headersDir = map (first relFile) $(FE.makeRelativeToProject "runtime/c/include" >>= FE.embedDir)
diff --git a/app/Commands/Compile/Wasi/Options.hs b/app/Commands/Compile/Wasi/Options.hs
index f9926a580..0686d457e 100644
--- a/app/Commands/Compile/Wasi/Options.hs
+++ b/app/Commands/Compile/Wasi/Options.hs
@@ -52,10 +52,10 @@ wasiHelperOptions opts =
           | otherwise = wasiReleaseRuntime
           where
             wasiReleaseRuntime :: BS.ByteString
-            wasiReleaseRuntime = $(FE.makeRelativeToProject "runtime/_build.wasm32-wasi/libjuvix.a" >>= FE.embedFile)
+            wasiReleaseRuntime = $(FE.makeRelativeToProject "runtime/c/_build.wasm32-wasi/libjuvix.a" >>= FE.embedFile)
 
             wasiDebugRuntime :: BS.ByteString
-            wasiDebugRuntime = $(FE.makeRelativeToProject "runtime/_build.wasm32-wasi-debug/libjuvix.a" >>= FE.embedFile)
+            wasiDebugRuntime = $(FE.makeRelativeToProject "runtime/c/_build.wasm32-wasi-debug/libjuvix.a" >>= FE.embedFile)
 
     wasiDefaultOutputFile :: Path Abs File -> Path Abs File -> Path Abs File
     wasiDefaultOutputFile inputFile baseOutputFile =
diff --git a/app/Commands/Extra/Compile.hs b/app/Commands/Extra/Compile.hs
index 725a29ac0..a743cda3b 100644
--- a/app/Commands/Extra/Compile.hs
+++ b/app/Commands/Extra/Compile.hs
@@ -58,16 +58,16 @@ prepareRuntime buildDir o = do
     AppTargetCairo -> return ()
   where
     wasiReleaseRuntime :: BS.ByteString
-    wasiReleaseRuntime = $(FE.makeRelativeToProject "runtime/_build.wasm32-wasi/libjuvix.a" >>= FE.embedFile)
+    wasiReleaseRuntime = $(FE.makeRelativeToProject "runtime/c/_build.wasm32-wasi/libjuvix.a" >>= FE.embedFile)
 
     nativeReleaseRuntime :: BS.ByteString
-    nativeReleaseRuntime = $(FE.makeRelativeToProject "runtime/_build.native64/libjuvix.a" >>= FE.embedFile)
+    nativeReleaseRuntime = $(FE.makeRelativeToProject "runtime/c/_build.native64/libjuvix.a" >>= FE.embedFile)
 
     wasiDebugRuntime :: BS.ByteString
-    wasiDebugRuntime = $(FE.makeRelativeToProject "runtime/_build.wasm32-wasi-debug/libjuvix.a" >>= FE.embedFile)
+    wasiDebugRuntime = $(FE.makeRelativeToProject "runtime/c/_build.wasm32-wasi-debug/libjuvix.a" >>= FE.embedFile)
 
     nativeDebugRuntime :: BS.ByteString
-    nativeDebugRuntime = $(FE.makeRelativeToProject "runtime/_build.native64-debug/libjuvix.a" >>= FE.embedFile)
+    nativeDebugRuntime = $(FE.makeRelativeToProject "runtime/c/_build.native64-debug/libjuvix.a" >>= FE.embedFile)
 
     writeRuntime :: BS.ByteString -> Sem r ()
     writeRuntime =
@@ -75,7 +75,7 @@ prepareRuntime buildDir o = do
         . BS.writeFile (toFilePath (buildDir <//> $(mkRelFile "libjuvix.a")))
 
     headersDir :: [(Path Rel File, BS.ByteString)]
-    headersDir = map (first relFile) $(FE.makeRelativeToProject "runtime/include" >>= FE.embedDir)
+    headersDir = map (first relFile) $(FE.makeRelativeToProject "runtime/c/include" >>= FE.embedDir)
 
     includeDir :: Path Abs Dir
     includeDir = juvixIncludeDir buildDir
diff --git a/cntlines.sh b/cntlines.sh
index 57686e0af..bd1e078c6 100755
--- a/cntlines.sh
+++ b/cntlines.sh
@@ -8,12 +8,13 @@ function count_ext () {
     find $2 -name $1 -print | xargs sed '/^[[:space:]]*$/d' | wc -l | tr -d ' '
 }
 
-RUNTIME_C=$(count runtime/src/juvix)
-RUNTIME_VAMPIR=$(count_ext '*.pir' runtime/src/vampir)
-RUNTIME_JVT=$(count_ext '*.jvt' runtime/src/tree)
-RUNTIME_CASM=$(count_ext '*.casm' runtime/src/casm)
+RUNTIME_C=$(count runtime/c/src/juvix)
+RUNTIME_RUST=$(count runtime/rust/src)
+RUNTIME_VAMPIR=$(count_ext '*.pir' runtime/vampir)
+RUNTIME_JVT=$(count_ext '*.jvt' runtime/tree)
+RUNTIME_CASM=$(count_ext '*.casm' runtime/casm)
 
-RUNTIME=$((RUNTIME_C+RUNTIME_VAMPIR+RUNTIME_JVT+RUNTIME_CASM))
+RUNTIME=$((RUNTIME_C+RUNTIME_RUST+RUNTIME_VAMPIR+RUNTIME_JVT+RUNTIME_CASM))
 
 BACKENDC=$(count src/Juvix/Compiler/Backend/C/)
 CAIRO=$(count src/Juvix/Compiler/Backend/Cairo/)
@@ -62,6 +63,7 @@ echo "   JuvixTree: $TREE LOC"
 echo "   JuvixCore: $CORE LOC"
 echo "Runtime: $RUNTIME LOC"
 echo "   C runtime: $RUNTIME_C LOC"
+echo "   Rust runtime: $RUNTIME_RUST LOC"
 echo "   JuvixTree runtime: $RUNTIME_JVT LOC"
 echo "   Cairo assembly runtime: $RUNTIME_CASM LOC"
 echo "   VampIR runtime: $RUNTIME_VAMPIR LOC"
@@ -74,4 +76,4 @@ echo "   Data: $DATA LOC"
 echo "   Prelude: $PRELUDE LOC"
 echo "Tests: $TESTS LOC"
 echo ""
-echo "Total: $TOTAL Haskell LOC + $RUNTIME_C C LOC + $RUNTIME_JVT JuvixTree LOC + $RUNTIME_CASM CASM LOC + $RUNTIME_VAMPIR VampIR LOC"
+echo "Total: $TOTAL Haskell LOC + $RUNTIME_C C LOC + $RUNTIME_RUST Rust LOC + $RUNTIME_JVT JuvixTree LOC + $RUNTIME_CASM CASM LOC + $RUNTIME_VAMPIR VampIR LOC"
diff --git a/justfile b/justfile
index ea621942c..55ca94dcc 100644
--- a/justfile
+++ b/justfile
@@ -104,7 +104,7 @@ run-profile +cmd:
 
 # Build the juvix runtime
 _buildRuntime:
-    cd runtime && make {{ runtimeArgs }} -j 4 -s
+    cd runtime && make {{ runtimeArgs }}
 
 # Build the project. `build runtime` builds only the runtime.
 [no-exit-message]
diff --git a/package.yaml b/package.yaml
index 6a8b8cf35..d6b9e831c 100644
--- a/package.yaml
+++ b/package.yaml
@@ -36,12 +36,12 @@ extra-source-files:
   - juvix-stdlib/**/*.juvix
   - include/package/**/*.juvix
   - include/package-base/**/*.juvix
-  - runtime/include/**/*.h
-  - runtime/**/*.a
-  - runtime/src/tree/*.jvt
-  - runtime/src/vampir/*.pir
-  - runtime/src/casm/*.casm
-  - runtime/src/nockma/*.nockma
+  - runtime/c/include/**/*.h
+  - runtime/c/**/*.a
+  - runtime/tree/*.jvt
+  - runtime/vampir/*.pir
+  - runtime/casm/*.casm
+  - runtime/nockma/*.nockma
 
 dependencies:
   - aeson-better-errors == 0.9.*
diff --git a/runtime/Makefile b/runtime/Makefile
index d8809dbad..fc99daaab 100644
--- a/runtime/Makefile
+++ b/runtime/Makefile
@@ -1,55 +1,21 @@
-all: release debug includes
 
-release: wasm32-wasi native64
+export
 
-debug: wasm32-wasi-debug native64-debug
+.PHONY: all
+all: juvix_c juvix_rust
 
-HEADERS := $(patsubst src/%,include/%,$(shell find src -name '*.h'))
+.PHONY: juvix_c
+juvix_c:
+	cd c && $(MAKE) -j 4 -s
 
-includes: $(HEADERS)
-
-$(HEADERS) : include/%.h : src/%.h
-	@mkdir -p `dirname $@`
-	@cp $< $@
-
-wasm32:
-	$(MAKE) -f Makefile.generic CONFIG=WASM32+RELEASE
-
-wasm32-wasi:
-	$(MAKE) -f Makefile.generic CONFIG=WASM32-WASI+RELEASE
-
-native32:
-	$(MAKE) -f Makefile.generic CONFIG=NATIVE32+RELEASE
-
-native64:
-	$(MAKE) -f Makefile.generic CONFIG=NATIVE64+RELEASE
-
-x86_32:
-	$(MAKE) -f Makefile.generic CONFIG=X86_32+RELEASE
-
-wasm32-debug:
-	$(MAKE) -f Makefile.generic CONFIG=WASM32+DEBUG
-
-wasm32-wasi-debug:
-	$(MAKE) -f Makefile.generic CONFIG=WASM32-WASI+DEBUG
-
-native32-debug:
-	$(MAKE) -f Makefile.generic CONFIG=NATIVE32+DEBUG
-
-native64-debug:
-	$(MAKE) -f Makefile.generic CONFIG=NATIVE64+DEBUG
-
-x86_32-debug:
-	$(MAKE) -f Makefile.generic CONFIG=X86_32+DEBUG
-
-asm:
-	$(MAKE) -f Makefile.generic CONFIG=ASM+DEBUG
-
-format:
-	@clang-format -i `find src -name '*.c' -or -name '*.h'`
+.PHONY: juvix_rust
+juvix_rust:
+	cd rust && cargo build --release
 
+.PHONY: clean
 clean:
-	@-rm -rf _build*
-	@-rm -rf include
+	cd c && $(MAKE) clean
 
-.PHONY: release debug includes wasm32 wasm32-wasi native32 native64 x86_32 wasm32-debug wasm32-wasi-debug native32-debug native64-debug x86_32-debug asm format clean
+.PHONY: format
+format:
+	cd c && $(MAKE) format
diff --git a/runtime/c/Makefile b/runtime/c/Makefile
new file mode 100644
index 000000000..4e67335d4
--- /dev/null
+++ b/runtime/c/Makefile
@@ -0,0 +1,56 @@
+all: release debug includes
+
+release: wasm32-wasi native64
+
+debug: wasm32-wasi-debug native64-debug
+
+HEADERS := $(patsubst src/%,include/%,$(shell find src -name '*.h'))
+CFORMAT := clang-format
+
+includes: $(HEADERS)
+
+$(HEADERS) : include/%.h : src/%.h
+	@mkdir -p `dirname $@`
+	@cp $< $@
+
+wasm32:
+	$(MAKE) -f Makefile.generic CONFIG=WASM32+RELEASE
+
+wasm32-wasi:
+	$(MAKE) -f Makefile.generic CONFIG=WASM32-WASI+RELEASE
+
+native32:
+	$(MAKE) -f Makefile.generic CONFIG=NATIVE32+RELEASE
+
+native64:
+	$(MAKE) -f Makefile.generic CONFIG=NATIVE64+RELEASE
+
+x86_32:
+	$(MAKE) -f Makefile.generic CONFIG=X86_32+RELEASE
+
+wasm32-debug:
+	$(MAKE) -f Makefile.generic CONFIG=WASM32+DEBUG
+
+wasm32-wasi-debug:
+	$(MAKE) -f Makefile.generic CONFIG=WASM32-WASI+DEBUG
+
+native32-debug:
+	$(MAKE) -f Makefile.generic CONFIG=NATIVE32+DEBUG
+
+native64-debug:
+	$(MAKE) -f Makefile.generic CONFIG=NATIVE64+DEBUG
+
+x86_32-debug:
+	$(MAKE) -f Makefile.generic CONFIG=X86_32+DEBUG
+
+asm:
+	$(MAKE) -f Makefile.generic CONFIG=ASM+DEBUG
+
+format:
+	@$(CFORMAT) -i `find src -name '*.c' -or -name '*.h'`
+
+clean:
+	@-rm -rf _build*
+	@-rm -rf include
+
+.PHONY: release debug includes wasm32 wasm32-wasi native32 native64 x86_32 wasm32-debug wasm32-wasi-debug native32-debug native64-debug x86_32-debug asm format clean
diff --git a/runtime/Makefile.generic b/runtime/c/Makefile.generic
similarity index 100%
rename from runtime/Makefile.generic
rename to runtime/c/Makefile.generic
diff --git a/runtime/PROJECT b/runtime/c/PROJECT
similarity index 100%
rename from runtime/PROJECT
rename to runtime/c/PROJECT
diff --git a/runtime/src/juvix/api.h b/runtime/c/src/juvix/api.h
similarity index 100%
rename from runtime/src/juvix/api.h
rename to runtime/c/src/juvix/api.h
diff --git a/runtime/src/juvix/arch/defs.h b/runtime/c/src/juvix/arch/defs.h
similarity index 100%
rename from runtime/src/juvix/arch/defs.h
rename to runtime/c/src/juvix/arch/defs.h
diff --git a/runtime/src/juvix/arch/wasi.c b/runtime/c/src/juvix/arch/wasi.c
similarity index 100%
rename from runtime/src/juvix/arch/wasi.c
rename to runtime/c/src/juvix/arch/wasi.c
diff --git a/runtime/src/juvix/arch/wasi.h b/runtime/c/src/juvix/arch/wasi.h
similarity index 100%
rename from runtime/src/juvix/arch/wasi.h
rename to runtime/c/src/juvix/arch/wasi.h
diff --git a/runtime/src/juvix/config.h b/runtime/c/src/juvix/config.h
similarity index 100%
rename from runtime/src/juvix/config.h
rename to runtime/c/src/juvix/config.h
diff --git a/runtime/src/juvix/defs.c b/runtime/c/src/juvix/defs.c
similarity index 100%
rename from runtime/src/juvix/defs.c
rename to runtime/c/src/juvix/defs.c
diff --git a/runtime/src/juvix/defs.h b/runtime/c/src/juvix/defs.h
similarity index 100%
rename from runtime/src/juvix/defs.h
rename to runtime/c/src/juvix/defs.h
diff --git a/runtime/src/juvix/funcall.h b/runtime/c/src/juvix/funcall.h
similarity index 100%
rename from runtime/src/juvix/funcall.h
rename to runtime/c/src/juvix/funcall.h
diff --git a/runtime/src/juvix/funcall/apply.h b/runtime/c/src/juvix/funcall/apply.h
similarity index 100%
rename from runtime/src/juvix/funcall/apply.h
rename to runtime/c/src/juvix/funcall/apply.h
diff --git a/runtime/src/juvix/funcall/funcall.h b/runtime/c/src/juvix/funcall/funcall.h
similarity index 100%
rename from runtime/src/juvix/funcall/funcall.h
rename to runtime/c/src/juvix/funcall/funcall.h
diff --git a/runtime/src/juvix/funcall/stacktrace.c b/runtime/c/src/juvix/funcall/stacktrace.c
similarity index 100%
rename from runtime/src/juvix/funcall/stacktrace.c
rename to runtime/c/src/juvix/funcall/stacktrace.c
diff --git a/runtime/src/juvix/funcall/stacktrace.h b/runtime/c/src/juvix/funcall/stacktrace.h
similarity index 100%
rename from runtime/src/juvix/funcall/stacktrace.h
rename to runtime/c/src/juvix/funcall/stacktrace.h
diff --git a/runtime/src/juvix/info.c b/runtime/c/src/juvix/info.c
similarity index 100%
rename from runtime/src/juvix/info.c
rename to runtime/c/src/juvix/info.c
diff --git a/runtime/src/juvix/info.h b/runtime/c/src/juvix/info.h
similarity index 100%
rename from runtime/src/juvix/info.h
rename to runtime/c/src/juvix/info.h
diff --git a/runtime/src/juvix/io.c b/runtime/c/src/juvix/io.c
similarity index 100%
rename from runtime/src/juvix/io.c
rename to runtime/c/src/juvix/io.c
diff --git a/runtime/src/juvix/io.h b/runtime/c/src/juvix/io.h
similarity index 100%
rename from runtime/src/juvix/io.h
rename to runtime/c/src/juvix/io.h
diff --git a/runtime/src/juvix/limits.h b/runtime/c/src/juvix/limits.h
similarity index 100%
rename from runtime/src/juvix/limits.h
rename to runtime/c/src/juvix/limits.h
diff --git a/runtime/src/juvix/mem.h b/runtime/c/src/juvix/mem.h
similarity index 100%
rename from runtime/src/juvix/mem.h
rename to runtime/c/src/juvix/mem.h
diff --git a/runtime/src/juvix/mem/alloc.c b/runtime/c/src/juvix/mem/alloc.c
similarity index 100%
rename from runtime/src/juvix/mem/alloc.c
rename to runtime/c/src/juvix/mem/alloc.c
diff --git a/runtime/src/juvix/mem/alloc.h b/runtime/c/src/juvix/mem/alloc.h
similarity index 100%
rename from runtime/src/juvix/mem/alloc.h
rename to runtime/c/src/juvix/mem/alloc.h
diff --git a/runtime/src/juvix/mem/gens.c b/runtime/c/src/juvix/mem/gens.c
similarity index 100%
rename from runtime/src/juvix/mem/gens.c
rename to runtime/c/src/juvix/mem/gens.c
diff --git a/runtime/src/juvix/mem/gens.h b/runtime/c/src/juvix/mem/gens.h
similarity index 100%
rename from runtime/src/juvix/mem/gens.h
rename to runtime/c/src/juvix/mem/gens.h
diff --git a/runtime/src/juvix/mem/mem.c b/runtime/c/src/juvix/mem/mem.c
similarity index 100%
rename from runtime/src/juvix/mem/mem.c
rename to runtime/c/src/juvix/mem/mem.c
diff --git a/runtime/src/juvix/mem/mem.h b/runtime/c/src/juvix/mem/mem.h
similarity index 100%
rename from runtime/src/juvix/mem/mem.h
rename to runtime/c/src/juvix/mem/mem.h
diff --git a/runtime/src/juvix/mem/pages.c b/runtime/c/src/juvix/mem/pages.c
similarity index 100%
rename from runtime/src/juvix/mem/pages.c
rename to runtime/c/src/juvix/mem/pages.c
diff --git a/runtime/src/juvix/mem/pages.h b/runtime/c/src/juvix/mem/pages.h
similarity index 100%
rename from runtime/src/juvix/mem/pages.h
rename to runtime/c/src/juvix/mem/pages.h
diff --git a/runtime/src/juvix/mem/stack.c b/runtime/c/src/juvix/mem/stack.c
similarity index 100%
rename from runtime/src/juvix/mem/stack.c
rename to runtime/c/src/juvix/mem/stack.c
diff --git a/runtime/src/juvix/mem/stack.h b/runtime/c/src/juvix/mem/stack.h
similarity index 100%
rename from runtime/src/juvix/mem/stack.h
rename to runtime/c/src/juvix/mem/stack.h
diff --git a/runtime/src/juvix/object.h b/runtime/c/src/juvix/object.h
similarity index 100%
rename from runtime/src/juvix/object.h
rename to runtime/c/src/juvix/object.h
diff --git a/runtime/src/juvix/object/boolean.h b/runtime/c/src/juvix/object/boolean.h
similarity index 100%
rename from runtime/src/juvix/object/boolean.h
rename to runtime/c/src/juvix/object/boolean.h
diff --git a/runtime/src/juvix/object/closure.c b/runtime/c/src/juvix/object/closure.c
similarity index 100%
rename from runtime/src/juvix/object/closure.c
rename to runtime/c/src/juvix/object/closure.c
diff --git a/runtime/src/juvix/object/closure.h b/runtime/c/src/juvix/object/closure.h
similarity index 100%
rename from runtime/src/juvix/object/closure.h
rename to runtime/c/src/juvix/object/closure.h
diff --git a/runtime/src/juvix/object/constr.h b/runtime/c/src/juvix/object/constr.h
similarity index 100%
rename from runtime/src/juvix/object/constr.h
rename to runtime/c/src/juvix/object/constr.h
diff --git a/runtime/src/juvix/object/cstring.c b/runtime/c/src/juvix/object/cstring.c
similarity index 100%
rename from runtime/src/juvix/object/cstring.c
rename to runtime/c/src/juvix/object/cstring.c
diff --git a/runtime/src/juvix/object/cstring.h b/runtime/c/src/juvix/object/cstring.h
similarity index 100%
rename from runtime/src/juvix/object/cstring.h
rename to runtime/c/src/juvix/object/cstring.h
diff --git a/runtime/src/juvix/object/equality.c b/runtime/c/src/juvix/object/equality.c
similarity index 100%
rename from runtime/src/juvix/object/equality.c
rename to runtime/c/src/juvix/object/equality.c
diff --git a/runtime/src/juvix/object/equality.h b/runtime/c/src/juvix/object/equality.h
similarity index 100%
rename from runtime/src/juvix/object/equality.h
rename to runtime/c/src/juvix/object/equality.h
diff --git a/runtime/src/juvix/object/integer.h b/runtime/c/src/juvix/object/integer.h
similarity index 100%
rename from runtime/src/juvix/object/integer.h
rename to runtime/c/src/juvix/object/integer.h
diff --git a/runtime/src/juvix/object/object.h b/runtime/c/src/juvix/object/object.h
similarity index 100%
rename from runtime/src/juvix/object/object.h
rename to runtime/c/src/juvix/object/object.h
diff --git a/runtime/src/juvix/object/print.c b/runtime/c/src/juvix/object/print.c
similarity index 100%
rename from runtime/src/juvix/object/print.c
rename to runtime/c/src/juvix/object/print.c
diff --git a/runtime/src/juvix/object/print.h b/runtime/c/src/juvix/object/print.h
similarity index 100%
rename from runtime/src/juvix/object/print.h
rename to runtime/c/src/juvix/object/print.h
diff --git a/runtime/src/juvix/opts.c b/runtime/c/src/juvix/opts.c
similarity index 100%
rename from runtime/src/juvix/opts.c
rename to runtime/c/src/juvix/opts.c
diff --git a/runtime/src/juvix/opts.h b/runtime/c/src/juvix/opts.h
similarity index 100%
rename from runtime/src/juvix/opts.h
rename to runtime/c/src/juvix/opts.h
diff --git a/runtime/src/casm/stdlib.casm b/runtime/casm/stdlib.casm
similarity index 100%
rename from runtime/src/casm/stdlib.casm
rename to runtime/casm/stdlib.casm
diff --git a/runtime/src/nockma/stdlib.nockma b/runtime/nockma/stdlib.nockma
similarity index 100%
rename from runtime/src/nockma/stdlib.nockma
rename to runtime/nockma/stdlib.nockma
diff --git a/runtime/rust/.gitignore b/runtime/rust/.gitignore
new file mode 100644
index 000000000..80aca6997
--- /dev/null
+++ b/runtime/rust/.gitignore
@@ -0,0 +1,3 @@
+/target
+Cargo.lock
+*~
diff --git a/runtime/rust/Cargo.toml b/runtime/rust/Cargo.toml
new file mode 100644
index 000000000..110ea8aa4
--- /dev/null
+++ b/runtime/rust/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "juvix"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/runtime/rust/src/apply.rs b/runtime/rust/src/apply.rs
new file mode 100644
index 000000000..e367550ee
--- /dev/null
+++ b/runtime/rust/src/apply.rs
@@ -0,0 +1,70 @@
+// Closure application
+
+use super::defs::*;
+use super::memory::*;
+
+pub enum AppResult {
+    // Call(fid)
+    Call(Word, Vec<Word>),
+    // Return(result_closure)
+    Return(Word),
+    // Continue(fid, args_left)
+    Continue(Word, Vec<Word>, Vec<Word>),
+}
+
+impl Memory {
+    pub fn apply(self: &mut Memory, cl: Word, cargs: &[Word]) -> AppResult {
+        let argsnum = self.get_closure_largs(cl);
+        if argsnum == cargs.len() {
+            let (fid, args) = self.call_closure(cl, cargs);
+            AppResult::Call(fid, args)
+        } else if argsnum > cargs.len() {
+            AppResult::Return(self.extend_closure(cl, cargs))
+        } else {
+            let (fid, args) = self.call_closure(cl, &cargs[0..argsnum]);
+            AppResult::Continue(fid, args, Vec::from(&cargs[argsnum..cargs.len()]))
+        }
+    }
+}
+
+#[macro_export]
+macro_rules! tapply {
+    ($lab:lifetime, $program:ident, $mem:ident, $fid:ident, $args:ident, $cl0:expr, $cargs0:expr) => {
+        let mut cl = $cl0;
+        let mut cargs = $cargs0;
+        loop {
+            match $mem.apply( cl, &cargs) {
+                apply::AppResult::Call(fid1, args1) => {
+                    $fid = fid1;
+                    $args = args1;
+                    continue $lab;
+                }
+                apply::AppResult::Return(r) => break $lab r,
+                apply::AppResult::Continue(fid1, args1, cargs1) => {
+                    cl = $program($mem, fid1, args1);
+                    cargs = cargs1;
+                }
+            }
+        }
+    };
+}
+
+#[macro_export]
+macro_rules! apply {
+    ($program:ident, $mem:ident, $cl0:expr, $cargs0:expr) => {{
+        let mut cl = $cl0;
+        let mut cargs = $cargs0;
+        loop {
+            match $mem.apply(cl, &cargs) {
+                apply::AppResult::Call(fid, args) => {
+                    break $program($mem, fid, args);
+                }
+                apply::AppResult::Return(r) => break r,
+                apply::AppResult::Continue(fid1, args1, cargs1) => {
+                    cl = $program($mem, fid1, args1);
+                    cargs = cargs1;
+                }
+            }
+        }
+    }};
+}
diff --git a/runtime/rust/src/closure.rs b/runtime/rust/src/closure.rs
new file mode 100644
index 000000000..328132afb
--- /dev/null
+++ b/runtime/rust/src/closure.rs
@@ -0,0 +1,130 @@
+// Closure manipulation
+
+use super::defs::*;
+use super::memory::*;
+
+pub const CLOSURE_HEADER_SIZE: usize = 3;
+
+impl Memory {
+    pub fn alloc_closure(self: &mut Memory, fid: Word, args: &[Word], largs: usize) -> Pointer {
+        let p = self.alloc(args.len() + CLOSURE_HEADER_SIZE);
+        self.set_closure_fid(p, fid);
+        self.set_closure_nargs(p, args.len());
+        self.set_closure_largs(p, largs);
+        self.set_closure_args(p, args);
+        p
+    }
+
+    pub fn extend_closure(self: &mut Memory, ptr: Pointer, args: &[Word]) -> Pointer {
+        let nargs = self.get_closure_nargs(ptr);
+        let p = self.alloc(nargs + args.len() + CLOSURE_HEADER_SIZE);
+        self.set_closure_fid(p, self.get_closure_fid(ptr));
+        self.set_closure_nargs(p, self.get_closure_nargs(ptr) + args.len());
+        self.set_closure_largs(p, self.get_closure_largs(ptr) - args.len());
+        let i1 = word_to_usize(ptr) + CLOSURE_HEADER_SIZE;
+        let i2 = word_to_usize(p) + CLOSURE_HEADER_SIZE;
+        for i in 0..nargs {
+            self[i2 + i] = self[i1 + i]
+        }
+        self[i2 + nargs..i2 + nargs + args.len()].copy_from_slice(args);
+        p
+    }
+
+    // Assigns stored closure args plus the provided closure args (`cargs`) to the
+    // argument space (`args`). Returns the function id to call.
+    pub fn call_closure(self: &Memory, cl: Word, cargs: &[Word]) -> (Word, Vec<Word>) {
+        let mut args = Vec::from(self.get_closure_args(cl));
+        args.extend(cargs);
+        return (self.get_closure_fid(cl), args);
+    }
+
+    // Function id
+    pub fn get_closure_fid(self: &Memory, ptr: Pointer) -> Word {
+        self[word_to_usize(ptr)]
+    }
+
+    // The number of arguments stored in the closure
+    pub fn get_closure_nargs(self: &Memory, ptr: Pointer) -> usize {
+        word_to_usize(self[word_to_usize(ptr) + 1])
+    }
+
+    // The number of arguments remaining for a call to the function
+    pub fn get_closure_largs(self: &Memory, ptr: Pointer) -> usize {
+        word_to_usize(self[word_to_usize(ptr) + 2])
+    }
+
+    pub fn get_closure_arg(self: &Memory, ptr: Pointer, idx: Word) -> Word {
+        self[word_to_usize(ptr) + CLOSURE_HEADER_SIZE + word_to_usize(idx)]
+    }
+
+    pub fn get_closure_args(self: &Memory, ptr: Pointer) -> &[Word] {
+        let i = word_to_usize(ptr) + CLOSURE_HEADER_SIZE;
+        let nargs = self.get_closure_nargs(ptr);
+        &self[i..i + nargs]
+    }
+
+    pub fn mut_closure_args(self: &mut Memory, ptr: Pointer) -> &mut [Word] {
+        let i = word_to_usize(ptr) + CLOSURE_HEADER_SIZE;
+        let nargs = self.get_closure_nargs(ptr);
+        &mut self[i..i + nargs]
+    }
+
+    pub fn set_closure_fid(self: &mut Memory, ptr: Pointer, uid: Word) {
+        self[word_to_usize(ptr)] = uid
+    }
+
+    pub fn set_closure_nargs(self: &mut Memory, ptr: Pointer, nargs: usize) {
+        self[word_to_usize(ptr) + 1] = usize_to_word(nargs)
+    }
+
+    pub fn set_closure_largs(self: &mut Memory, ptr: Pointer, largs: usize) {
+        self[word_to_usize(ptr) + 2] = usize_to_word(largs)
+    }
+
+    pub fn set_closure_arg(self: &mut Memory, ptr: Pointer, idx: Word, x: Word) {
+        self[word_to_usize(ptr) + CLOSURE_HEADER_SIZE + word_to_usize(idx)] = x
+    }
+
+    pub fn set_closure_args(self: &mut Memory, ptr: Pointer, args: &[Word]) {
+        self.mut_closure_args(ptr).copy_from_slice(args);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_closures() {
+        let mut mem = Memory::new();
+        for fid in 0..10 {
+            for k in 0..100 {
+                let args: Vec<Word> = (0..k).collect();
+                let largs = (k / 2) as usize;
+                let cl = mem.alloc_closure(fid, &args, largs);
+                assert_eq!(mem.get_closure_fid(cl), fid);
+                assert_eq!(mem.get_closure_nargs(cl), args.len());
+                assert_eq!(mem.get_closure_largs(cl), largs);
+                assert_eq!(mem.get_closure_args(cl), args);
+                mem.set_closure_fid(cl, fid + 1);
+                assert_eq!(mem.get_closure_fid(cl), fid + 1);
+                if k > 0 {
+                    mem.set_closure_arg(cl, k / 2, 789);
+                    assert_eq!(mem.get_closure_arg(cl, k / 2), 789);
+                }
+                if largs > 1 {
+                    let n: Word = k + largs as Word - 1;
+                    let args1: Vec<Word> = (k..n).collect();
+                    let cl1 = mem.extend_closure(cl, &args1);
+                    let mut args2: Vec<Word> = (0..n).collect();
+                    if k > 0 {
+                        args2[(k / 2) as usize] = 789;
+                    }
+                    assert_eq!(mem.get_closure_args(cl1), args2);
+                    assert_eq!(mem.get_closure_nargs(cl1), args2.len());
+                    assert_eq!(mem.get_closure_largs(cl1), 1);
+                }
+            }
+        }
+    }
+}
diff --git a/runtime/rust/src/constr.rs b/runtime/rust/src/constr.rs
new file mode 100644
index 000000000..7702f4164
--- /dev/null
+++ b/runtime/rust/src/constr.rs
@@ -0,0 +1,80 @@
+// Constructor access and manipulation
+
+use super::defs::*;
+use super::memory::*;
+
+pub const CONSTR_HEADER_SIZE: usize = 2;
+
+impl Memory {
+    pub fn alloc_constr(self: &mut Memory, tag: Word, args: &[Word]) -> Pointer {
+        let p = self.alloc(args.len() + CONSTR_HEADER_SIZE);
+        self.set_constr_tag(p, tag);
+        self.set_constr_nargs(p, args.len());
+        self.set_constr_args(p, args);
+        p
+    }
+
+    pub fn get_constr_tag(self: &Memory, ptr: Pointer) -> Word {
+        self[word_to_usize(ptr)]
+    }
+
+    pub fn get_constr_nargs(self: &Memory, ptr: Pointer) -> usize {
+        word_to_usize(self[word_to_usize(ptr) + 1])
+    }
+
+    pub fn get_constr_arg(self: &Memory, ptr: Pointer, idx: Word) -> Word {
+        self[word_to_usize(ptr) + CONSTR_HEADER_SIZE + word_to_usize(idx)]
+    }
+
+    pub fn get_constr_args(self: &Memory, ptr: Pointer) -> &[Word] {
+        let i = word_to_usize(ptr) + CONSTR_HEADER_SIZE;
+        let nargs = self.get_constr_nargs(ptr);
+        &self[i..i + nargs]
+    }
+
+    pub fn mut_constr_args(self: &mut Memory, ptr: Pointer) -> &mut [Word] {
+        let i = word_to_usize(ptr) + CONSTR_HEADER_SIZE;
+        let nargs = self.get_constr_nargs(ptr);
+        &mut self[i..i + nargs]
+    }
+
+    pub fn set_constr_tag(self: &mut Memory, ptr: Pointer, tag: Word) {
+        self[word_to_usize(ptr)] = tag
+    }
+
+    pub fn set_constr_nargs(self: &mut Memory, ptr: Pointer, nfields: usize) {
+        self[word_to_usize(ptr) + 1] = usize_to_word(nfields)
+    }
+
+    pub fn set_constr_arg(self: &mut Memory, ptr: Pointer, idx: Word, x: Word) {
+        self[word_to_usize(ptr) + CONSTR_HEADER_SIZE + word_to_usize(idx)] = x
+    }
+
+    pub fn set_constr_args(self: &mut Memory, ptr: Pointer, args: &[Word]) {
+        self.mut_constr_args(ptr).copy_from_slice(args);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_constrs() {
+        let mut mem = Memory::new();
+        for tag in 0..10 {
+            for k in 0..100 {
+                let args: Vec<Word> = (0..k).collect();
+                let ctr = mem.alloc_constr(tag, &args);
+                assert_eq!(mem.get_constr_tag(ctr), tag);
+                assert_eq!(mem.get_constr_args(ctr), args);
+                mem.set_constr_tag(ctr, tag + 1);
+                assert_eq!(mem.get_constr_tag(ctr), tag + 1);
+                if k > 0 {
+                    mem.set_constr_arg(ctr, k / 2, 789);
+                    assert_eq!(mem.get_constr_arg(ctr, k / 2), 789);
+                }
+            }
+        }
+    }
+}
diff --git a/runtime/rust/src/defs.rs b/runtime/rust/src/defs.rs
new file mode 100644
index 000000000..f6d8ded99
--- /dev/null
+++ b/runtime/rust/src/defs.rs
@@ -0,0 +1,33 @@
+// Runtime definitions
+
+// Type of words
+pub type Word = u32;
+
+// Type of pointers
+pub type Pointer = Word;
+
+// Type of signed small integers that fit into a single word
+pub type SmallInt = i32;
+
+pub const INITIAL_STACK_CAPACITY: usize = 10 * 1024;
+pub const INITIAL_MEMORY_CAPACITY: usize = 10 * 1024;
+
+pub fn word_to_usize(s: Word) -> usize {
+    s as usize
+}
+
+pub fn usize_to_word(s: usize) -> Word {
+    s as Word
+}
+
+pub fn bool_to_word(x: bool) -> Word {
+    x as Word
+}
+
+pub fn word_to_bool(x: Word) -> bool {
+    if x == 0 {
+        false
+    } else {
+        true
+    }
+}
diff --git a/runtime/rust/src/equality.rs b/runtime/rust/src/equality.rs
new file mode 100644
index 000000000..cce7c53fc
--- /dev/null
+++ b/runtime/rust/src/equality.rs
@@ -0,0 +1,9 @@
+// Equality
+
+use super::defs::*;
+
+// Check for equality. The implementation is incorrect for complex objects, but
+// complex objects are not compared in Juvix with built-in equality for now.
+pub fn juvix_equal(x: Word, y: Word) -> bool {
+    x == y
+}
diff --git a/runtime/rust/src/integer.rs b/runtime/rust/src/integer.rs
new file mode 100644
index 000000000..c68332ef7
--- /dev/null
+++ b/runtime/rust/src/integer.rs
@@ -0,0 +1,68 @@
+// Integers
+
+use super::defs::*;
+
+pub fn make_smallint(x: SmallInt) -> Word {
+    x as Word
+}
+
+pub fn smallint_value(x: Word) -> SmallInt {
+    x as SmallInt
+}
+
+pub fn smallint_add(x: Word, y: Word) -> Word {
+    x + y
+}
+
+pub fn smallint_sub(x: Word, y: Word) -> Word {
+    make_smallint(smallint_value(x) - smallint_value(y))
+}
+
+pub fn smallint_mul(x: Word, y: Word) -> Word {
+    make_smallint(smallint_value(x) * smallint_value(y))
+}
+
+pub fn smallint_div(x: Word, y: Word) -> Word {
+    make_smallint(smallint_value(x) / smallint_value(y))
+}
+
+pub fn smallint_mod(x: Word, y: Word) -> Word {
+    make_smallint(smallint_value(x) % smallint_value(y))
+}
+
+pub fn smallint_lt(x: Word, y: Word) -> Word {
+    bool_to_word(smallint_value(x) < smallint_value(y))
+}
+
+pub fn smallint_le(x: Word, y: Word) -> Word {
+    bool_to_word(smallint_value(x) <= smallint_value(y))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_integer_conversion() {
+        for x in 0..100 {
+            assert_eq!(smallint_value(make_smallint(x)), x);
+        }
+    }
+
+    #[test]
+    fn test_integer_arithmetic() {
+        for x in 1..100 {
+            let y = smallint_div(
+                smallint_mul(
+                    smallint_sub(
+                        smallint_add(make_smallint(x), make_smallint(4)),
+                        make_smallint(4),
+                    ),
+                    make_smallint(7),
+                ),
+                make_smallint(7),
+            );
+            assert_eq!(make_smallint(x), y);
+        }
+    }
+}
diff --git a/runtime/rust/src/lib.rs b/runtime/rust/src/lib.rs
new file mode 100644
index 000000000..40e8753ff
--- /dev/null
+++ b/runtime/rust/src/lib.rs
@@ -0,0 +1,238 @@
+#[macro_use]
+pub mod apply;
+pub mod closure;
+pub mod constr;
+pub mod defs;
+pub mod equality;
+pub mod integer;
+pub mod memory;
+
+#[cfg(test)]
+mod tests {
+    use super::apply;
+    use super::defs::*;
+    use super::equality::*;
+    use super::integer::*;
+    use super::memory::*;
+
+    #[allow(unused_mut)]
+    fn program_fib(mut fid: Word, args: Vec<Word>) -> Word {
+        const FUN_FIB: Word = 0;
+        loop {
+            match fid {
+                FUN_FIB => {
+                    #[allow(unused_mut)]
+                    let mut tmp1: Word;
+                    #[allow(unused_mut)]
+                    let mut tmp2: Word;
+                    if word_to_bool(smallint_le(args[0], make_smallint(1))) {
+                        break args[0];
+                    } else {
+                        tmp1 = program_fib(FUN_FIB, vec![smallint_sub(args[0], make_smallint(1))]);
+                        tmp2 = program_fib(FUN_FIB, vec![smallint_sub(args[0], make_smallint(2))]);
+                        break (smallint_add(tmp1, tmp2));
+                    }
+                }
+                _ => panic!("unknown function id"),
+            }
+        }
+    }
+
+    fn program_itfib(mut fid: Word, mut args: Vec<Word>) -> Word {
+        const FUN_ITFIB: Word = 0;
+        const FUN_ITFIB_GO: Word = 1;
+        loop {
+            match fid {
+                FUN_ITFIB => {
+                    args = vec![args[0], 0, 1];
+                    fid = FUN_ITFIB_GO;
+                    continue;
+                }
+                FUN_ITFIB_GO => {
+                    if juvix_equal(args[0], make_smallint(0)) {
+                        break args[1];
+                    } else {
+                        args = vec![
+                            smallint_sub(args[0], make_smallint(1)),
+                            args[2],
+                            smallint_add(args[1], args[2]),
+                        ];
+                        fid = FUN_ITFIB_GO;
+                        continue;
+                    }
+                }
+                _ => panic!("unknown function id"),
+            }
+        }
+    }
+
+    fn program_closure_call(mem: &mut Memory, mut fid: Word, mut args: Vec<Word>) -> Word {
+        const FUN_MAIN: Word = 0;
+        const FUN_CALCULATE: Word = 1;
+        const FUN_APPLY_1: Word = 2;
+        loop {
+            match fid {
+                FUN_MAIN => {
+                    args[0] =
+                        mem.alloc_closure(FUN_CALCULATE, &[make_smallint(5), make_smallint(3)], 1);
+                    fid = FUN_APPLY_1;
+                    continue;
+                }
+                FUN_CALCULATE => {
+                    #[allow(unused_mut)]
+                    let mut tmp1: Word;
+                    tmp1 = smallint_mul(args[2], args[1]);
+                    tmp1 = smallint_add(args[0], tmp1);
+                    return tmp1;
+                }
+                FUN_APPLY_1 => {
+                    (fid, args) = mem.call_closure(args[0], &[make_smallint(2)]);
+                    continue;
+                }
+                _ => panic!("unknown function id"),
+            }
+        }
+    }
+
+    fn program_sk(mem: &mut Memory, mut fid: Word, mut args: Vec<Word>) -> Word {
+        const FUN_MAIN: Word = 0;
+        const FUN_S: Word = 1;
+        const FUN_K: Word = 2;
+        const FUN_I: Word = 3;
+        'program: loop {
+            match fid {
+                FUN_MAIN => {
+                    let id = program_sk(mem, FUN_I, vec![]);
+                    let x = apply!(
+                        program_sk,
+                        mem,
+                        id,
+                        vec![id, id, id, id, id, id, make_smallint(1)]
+                    );
+                    let y = apply!(
+                        program_sk,
+                        mem,
+                        id,
+                        vec![id, id, id, id, id, id, id, id, id, make_smallint(1)]
+                    );
+                    let z = apply!(
+                        program_sk,
+                        mem,
+                        id,
+                        vec![id, id, id, id, id, id, id, id, id, id, id, make_smallint(1)]
+                    );
+                    let tmp1 = smallint_add(x, y);
+                    break smallint_add(tmp1, z);
+                }
+                FUN_S => {
+                    let xz = apply!(program_sk, mem, args[0], vec![args[2]]);
+                    let yz = apply!(program_sk, mem, args[1], vec![args[2]]);
+                    tapply!('program, program_sk, mem, fid, args, xz, vec![yz]);
+                }
+                FUN_K => {
+                    break args[0];
+                }
+                FUN_I => {
+                    let k = mem.alloc_closure(FUN_K, &[], 2);
+                    break mem.alloc_closure(FUN_S, &[k, k], 1);
+                }
+                _ => panic!("unknown function id"),
+            }
+        }
+    }
+
+    #[allow(unused_mut)]
+    fn program_lists(mem: &mut Memory, mut fid: Word, mut args: Vec<Word>) -> Word {
+        const FUN_MAIN: Word = 0;
+        const FUN_MAP: Word = 1;
+        const FUN_ADD_ONE: Word = 2;
+        const FUN_SUM: Word = 3;
+        const FUN_GEN: Word = 4;
+        const TAG_NIL: Word = 0;
+        const TAG_CONS: Word = 1;
+        loop {
+            match fid {
+                FUN_MAIN => {
+                    let lst1 = program_lists(mem, FUN_GEN, vec![make_smallint(1000)]);
+                    let inc = mem.alloc_closure(FUN_ADD_ONE, &[], 1);
+                    let lst2 = program_lists(mem, FUN_MAP, vec![inc, lst1]);
+                    return program_lists(mem, FUN_SUM, vec![lst2]);
+                }
+                FUN_MAP => match mem.get_constr_tag(args[1]) {
+                    TAG_NIL => {
+                        return args[1];
+                    }
+                    TAG_CONS => {
+                        let h = apply!(
+                            program_lists,
+                            mem,
+                            args[0],
+                            vec![mem.get_constr_arg(args[1], 0)]
+                        );
+                        let t = program_lists(
+                            mem,
+                            FUN_MAP,
+                            vec![args[0], mem.get_constr_arg(args[1], 1)],
+                        );
+                        return mem.alloc_constr(TAG_CONS, &[h, t]);
+                    }
+                    _ => panic!("unknown constructor tag"),
+                },
+                FUN_ADD_ONE => {
+                    return smallint_add(args[0], make_smallint(1));
+                }
+                FUN_SUM => match mem.get_constr_tag(args[0]) {
+                    TAG_NIL => return make_smallint(0),
+                    TAG_CONS => {
+                        let s = program_lists(mem, FUN_SUM, vec![mem.get_constr_arg(args[0], 1)]);
+                        return smallint_add(s, mem.get_constr_arg(args[0], 0));
+                    }
+                    _ => panic!("unknown constructor tag"),
+                },
+                FUN_GEN => {
+                    if args[0] == make_smallint(0) {
+                        return mem.alloc_constr(TAG_NIL, &[]);
+                    } else {
+                        let t = program_lists(
+                            mem,
+                            FUN_GEN,
+                            vec![smallint_sub(args[0], make_smallint(1))],
+                        );
+                        return mem.alloc_constr(TAG_CONS, &[args[0], t]);
+                    }
+                }
+                _ => panic!("unknown function id"),
+            }
+        }
+    }
+
+    #[test]
+    fn test_fib() {
+        let result = program_fib(0, vec![11]);
+        assert_eq!(result, 89);
+    }
+
+    #[test]
+    fn test_itfib() {
+        let result = program_itfib(0, vec![11, 0, 0]);
+        assert_eq!(result, 89);
+    }
+
+    #[test]
+    fn test_closure_call() {
+        let result = program_closure_call(&mut Memory::new(), 0, vec![0, 0, 0]);
+        assert_eq!(result, 11);
+    }
+
+    #[test]
+    fn test_sk() {
+        let result = program_sk(&mut Memory::new(), 0, vec![]);
+        assert_eq!(result, 3);
+    }
+
+    #[test]
+    fn test_lists() {
+        let result = program_lists(&mut Memory::new(), 0, vec![]);
+        assert_eq!(result, 501500);
+    }
+}
diff --git a/runtime/rust/src/memory.rs b/runtime/rust/src/memory.rs
new file mode 100644
index 000000000..5512b5ee4
--- /dev/null
+++ b/runtime/rust/src/memory.rs
@@ -0,0 +1,61 @@
+// Heap memory management
+
+use super::defs::*;
+
+pub struct Memory {
+    memory: Vec<Word>,
+}
+
+impl Memory {
+    pub fn new() -> Self {
+        Self {
+            memory: Vec::with_capacity(INITIAL_MEMORY_CAPACITY),
+        }
+    }
+
+    pub fn alloc(&mut self, size: usize) -> Pointer {
+        let idx = self.memory.len();
+        self.memory.resize(idx + size, 0);
+        idx as Pointer
+    }
+}
+
+impl<Idx> std::ops::Index<Idx> for Memory
+where
+    Idx: std::slice::SliceIndex<[Word]>,
+{
+    type Output = Idx::Output;
+
+    fn index(&self, index: Idx) -> &Self::Output {
+        &self.memory[index]
+    }
+}
+
+impl<Idx> std::ops::IndexMut<Idx> for Memory
+where
+    Idx: std::slice::SliceIndex<[Word]>,
+{
+    fn index_mut(&mut self, index: Idx) -> &mut Self::Output {
+        &mut self.memory[index]
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_memory() {
+        let mut mem = Memory::new();
+        for k in 0..100 {
+            let p = mem.alloc(1000);
+            for j in 1..1001 {
+                mem[(p + j - 1) as usize] = k * 1000 + j;
+                assert_eq!(mem[(p + j - 1) as usize], k * 1000 + j);
+            }
+        }
+        for i in 0..100_000 {
+            assert_eq!(mem[i as usize], i + 1);
+        }
+    }
+}
diff --git a/runtime/src/tree/apply.jvt b/runtime/tree/apply.jvt
similarity index 100%
rename from runtime/src/tree/apply.jvt
rename to runtime/tree/apply.jvt
diff --git a/runtime/src/vampir/stdlib.pir b/runtime/vampir/stdlib.pir
similarity index 100%
rename from runtime/src/vampir/stdlib.pir
rename to runtime/vampir/stdlib.pir
diff --git a/runtime/src/vampir/stdlib_unsafe.pir b/runtime/vampir/stdlib_unsafe.pir
similarity index 100%
rename from runtime/src/vampir/stdlib_unsafe.pir
rename to runtime/vampir/stdlib_unsafe.pir
diff --git a/src/Juvix/Compiler/Backend/VampIR/Pretty/Base.hs b/src/Juvix/Compiler/Backend/VampIR/Pretty/Base.hs
index 4c05c0286..82136d327 100644
--- a/src/Juvix/Compiler/Backend/VampIR/Pretty/Base.hs
+++ b/src/Juvix/Compiler/Backend/VampIR/Pretty/Base.hs
@@ -103,9 +103,9 @@ vampIRDefs bits unsafe =
     <> ";\n\n"
     <> if
         | unsafe ->
-            UTF8.toString $(FE.makeRelativeToProject ("runtime/src/vampir/stdlib_unsafe" <> vampIRFileExt) >>= FE.embedFile)
+            UTF8.toString $(FE.makeRelativeToProject ("runtime/vampir/stdlib_unsafe" <> vampIRFileExt) >>= FE.embedFile)
         | otherwise ->
-            UTF8.toString $(FE.makeRelativeToProject ("runtime/src/vampir/stdlib" <> vampIRFileExt) >>= FE.embedFile)
+            UTF8.toString $(FE.makeRelativeToProject ("runtime/vampir/stdlib" <> vampIRFileExt) >>= FE.embedFile)
 
 --------------------------------------------------------------------------------
 -- helper functions
diff --git a/src/Juvix/Compiler/Casm/Extra/Stdlib.hs b/src/Juvix/Compiler/Casm/Extra/Stdlib.hs
index 37ca26c9a..246aacd84 100644
--- a/src/Juvix/Compiler/Casm/Extra/Stdlib.hs
+++ b/src/Juvix/Compiler/Casm/Extra/Stdlib.hs
@@ -30,7 +30,7 @@ addStdlibBuiltins addr = do
   instrs <-
     fmap (fromRight impossible) $
       runParser' addr "stdlib.casm" $
-        decodeUtf8 $(FE.makeRelativeToProject "runtime/src/casm/stdlib.casm" >>= FE.embedFile)
+        decodeUtf8 $(FE.makeRelativeToProject "runtime/casm/stdlib.casm" >>= FE.embedFile)
   let _stdlibGetRegsName :: Text = "juvix_get_regs"
       _stdlibCallClosureName :: Text = "juvix_call_closure"
       _stdlibExtendClosureName :: Text = "juvix_extend_closure"
diff --git a/src/Juvix/Compiler/Nockma/Stdlib.hs b/src/Juvix/Compiler/Nockma/Stdlib.hs
index 83705a5a5..b58618be4 100644
--- a/src/Juvix/Compiler/Nockma/Stdlib.hs
+++ b/src/Juvix/Compiler/Nockma/Stdlib.hs
@@ -8,4 +8,4 @@ stdlib :: Term Natural
 stdlib =
   fromRight impossible $
     parseText $
-      decodeUtf8 $(FE.makeRelativeToProject "runtime/src/nockma/stdlib.nockma" >>= FE.embedFile)
+      decodeUtf8 $(FE.makeRelativeToProject "runtime/nockma/stdlib.nockma" >>= FE.embedFile)
diff --git a/src/Juvix/Compiler/Tree/Extra/Apply.hs b/src/Juvix/Compiler/Tree/Extra/Apply.hs
index abc546383..d1e490547 100644
--- a/src/Juvix/Compiler/Tree/Extra/Apply.hs
+++ b/src/Juvix/Compiler/Tree/Extra/Apply.hs
@@ -27,7 +27,7 @@ addApplyBuiltins tab = (blts, bs' ^. stateInfoTable)
     bs' =
       fromRight impossible $
         parseText' bs $
-          decodeUtf8 $(FE.makeRelativeToProject "runtime/src/tree/apply.jvt" >>= FE.embedFile)
+          decodeUtf8 $(FE.makeRelativeToProject "runtime/tree/apply.jvt" >>= FE.embedFile)
 
     blts :: ApplyBuiltins
     blts =
diff --git a/test/Runtime/Base.hs b/test/Runtime/Base.hs
index 455122168..867565443 100644
--- a/test/Runtime/Base.hs
+++ b/test/Runtime/Base.hs
@@ -99,7 +99,7 @@ commonArgs outputFile =
   ]
   where
     runtimeInclude :: FilePath
-    runtimeInclude = $(makeRelativeToProject "runtime/include" >>= strToExp)
+    runtimeInclude = $(makeRelativeToProject "runtime/c/include" >>= strToExp)
 
 native64Args :: Int -> Path Abs File -> Path Abs File -> [String]
 native64Args optLevel outputFile inputFile =
@@ -115,7 +115,7 @@ native64Args optLevel outputFile inputFile =
        ]
   where
     juvixLibraryDir :: FilePath
-    juvixLibraryDir = $(makeRelativeToProject "runtime/_build.native64-debug" >>= strToExp)
+    juvixLibraryDir = $(makeRelativeToProject "runtime/c/_build.native64-debug" >>= strToExp)
 
 wasiArgs :: Int -> Path Abs Dir -> Path Abs File -> Path Abs File -> [String]
 wasiArgs optLevel sysrootPath outputFile inputFile =
@@ -134,4 +134,4 @@ wasiArgs optLevel sysrootPath outputFile inputFile =
        ]
   where
     juvixLibraryDir :: Path Abs Dir
-    juvixLibraryDir = absDir $(makeRelativeToProject "runtime/_build.wasm32-wasi-debug" >>= strToExp)
+    juvixLibraryDir = absDir $(makeRelativeToProject "runtime/c/_build.wasm32-wasi-debug" >>= strToExp)