diff --git a/integration_tests/format_test.ucg b/integration_tests/format_test.ucg
new file mode 100644
index 0000000..e2d825f
--- /dev/null
+++ b/integration_tests/format_test.ucg
@@ -0,0 +1,4 @@
+assert |"hello @" % ("world") == "hello world"|;
+assert |"1 @ @" % (2, 3) == "1 2 3"|;
+assert |"@ or @" % (true, false) == "true or false"|;
+assert |"@" % (NULL) == "NULL"|;
\ No newline at end of file
diff --git a/src/build/compile_test.rs b/src/build/compile_test.rs
index f893ac1..00495c0 100644
--- a/src/build/compile_test.rs
+++ b/src/build/compile_test.rs
@@ -73,3 +73,8 @@ fn test_concatenation() {
         "../../integration_tests/concatenation_test.ucg"
     ));
 }
+
+#[test]
+fn test_format() {
+    assert_build(include_str!("../../integration_tests/format_test.ucg"));
+}
diff --git a/src/build/mod.rs b/src/build/mod.rs
index 0e19110..32152a9 100644
--- a/src/build/mod.rs
+++ b/src/build/mod.rs
@@ -276,6 +276,8 @@ impl From<Val> for String {
             Val::Int(ref i) => format!("{}", i),
             Val::Float(ref f) => format!("{}", f),
             Val::Str(ref s) => s.to_string(),
+            Val::Boolean(ref b) => format!("{}", b),
+            Val::Empty => "NULL".to_string(),
             val => format!("<{}>", val),
         }
     }