diff --git a/lib/eval.c b/lib/eval.c
index 7507175..a4c7936 100644
--- a/lib/eval.c
+++ b/lib/eval.c
@@ -4,9 +4,8 @@
 
 #include <assert.h>
 
-void eval(am_t *am)
+static void eval_atom(am_t *am)
 {
-	assert(am->expr->is_atom);
 	switch (am->expr->atom.type) {
 	case ATOM_TYPE_EMPTY_LIST:
 	case ATOM_TYPE_INTEGER:
@@ -18,3 +17,26 @@ void eval(am_t *am)
 		break;
 	}
 }
+
+static void eval_list(am_t *am)
+{
+	am->argl = am->expr->pair.cdr;
+	am->expr = am->expr->pair.car;
+
+	assert(am->expr->is_atom);
+	assert(am->expr->atom.type == ATOM_TYPE_SYMBOL);
+	env_fetch(am);
+
+	assert(am->val->is_atom);
+	assert(am->val->atom.type == ATOM_TYPE_PRIM_PROC);
+	assert(am->val->atom.prim_proc != NULL);
+	am->val->atom.prim_proc(am);
+}
+
+void eval(am_t *am)
+{
+	if (am->expr->is_atom)
+		eval_atom(am);
+	else
+		eval_list(am);
+}
diff --git a/tests/eval_tests.c b/tests/eval_tests.c
index bc23c63..0a3934b 100644
--- a/tests/eval_tests.c
+++ b/tests/eval_tests.c
@@ -69,6 +69,25 @@ static void test_foo_evals_to_42_when_set_in_env(void)
 	TEST_ASSERT_EQUAL(42, am.val->atom.integer);
 }
 
+static void test_add_1_2_3_evals_to_6(void)
+{
+	am.expr = expr_pair(
+	    &am, expr_str_symbol(&am, "+"),
+	    expr_pair(
+	        &am, expr_integer(&am, 1),
+	        expr_pair(
+	            &am, expr_integer(&am, 2),
+	            expr_pair(
+	                &am, expr_integer(&am, 3), expr_empty_list(&am)))));
+
+	eval(&am);
+
+	TEST_ASSERT_NOT_NULL(am.val);
+	TEST_ASSERT_TRUE(am.val->is_atom);
+	TEST_ASSERT_EQUAL(ATOM_TYPE_INTEGER, am.val->atom.type);
+	TEST_ASSERT_EQUAL(6, am.val->atom.integer);
+}
+
 int main(void)
 {
 	UNITY_BEGIN();
@@ -76,5 +95,6 @@ int main(void)
 	RUN_TEST(test_empty_list_self_evals);
 	RUN_TEST(test_prim_proc_self_evals);
 	RUN_TEST(test_foo_evals_to_42_when_set_in_env);
+	RUN_TEST(test_add_1_2_3_evals_to_6);
 	return UNITY_END();
 }