diff --git a/lib/CMakeLists.txt b/lib/CMakeLists.txt
index 3055247..2c31a8d 100644
--- a/lib/CMakeLists.txt
+++ b/lib/CMakeLists.txt
@@ -1,4 +1,5 @@
 add_library(imp
+  am.c
   memory_stream.c
   store.c
   token.c
diff --git a/lib/am.c b/lib/am.c
new file mode 100644
index 0000000..65ee9f1
--- /dev/null
+++ b/lib/am.c
@@ -0,0 +1,22 @@
+#include "am.h"
+
+#include <assert.h>
+#include <string.h>
+
+void am_init(am_t *am)
+{
+	memset(am, 0, sizeof(am_t));
+	am->sp = am->stack + AM_STACK_SIZE - 1;
+}
+
+void am_push(am_t *am)
+{
+	assert(am->sp >= am->stack);
+	*am->sp-- = am->expr;
+}
+
+void am_pop(am_t *am)
+{
+	assert(am->sp < am->stack + AM_STACK_SIZE - 1);
+	am->expr = *++am->sp;
+}
diff --git a/lib/include/am.h b/lib/include/am.h
new file mode 100644
index 0000000..eb96ddd
--- /dev/null
+++ b/lib/include/am.h
@@ -0,0 +1,17 @@
+#ifndef AM_H
+#define AM_H
+
+#include "expr.h"
+
+#define AM_STACK_SIZE 128U
+
+typedef struct {
+	expr_t *expr;
+	expr_t **sp, *stack[AM_STACK_SIZE];
+} am_t;
+
+void am_init(am_t *am);
+void am_push(am_t *am);
+void am_pop(am_t *am);
+
+#endif
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index ddf0a5f..439cb1a 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -9,6 +9,7 @@ function(add_test_suites)
 endfunction()
 
 add_test_suites(
+  am_tests.c
   store_tests.c
   token_tests.c
 )
diff --git a/tests/am_tests.c b/tests/am_tests.c
new file mode 100644
index 0000000..a64f82c
--- /dev/null
+++ b/tests/am_tests.c
@@ -0,0 +1,30 @@
+#include "am.h"
+#include "unity.h"
+
+static am_t am;
+
+void setUp(void)
+{
+	am_init(&am);
+}
+
+void tearDown(void)
+{
+}
+
+static void test_expr_value_restored_after_push_modify_pop(void)
+{
+	expr_t a, b;
+	am.expr = &a;
+	am_push(&am);
+	am.expr = &b;
+	am_pop(&am);
+	TEST_ASSERT_EQUAL(&a, am.expr);
+}
+
+int main(void)
+{
+	UNITY_BEGIN();
+	RUN_TEST(test_expr_value_restored_after_push_modify_pop);
+	return UNITY_END();
+}