diff --git a/src/builtins.c b/src/builtins.c
index c78eeee..abb0010 100644
--- a/src/builtins.c
+++ b/src/builtins.c
@@ -8,10 +8,6 @@
 #include <string.h>
 #include <stdlib.h>
 
-LISP_FUNC_0(ucl_builtin_hello_world) {
-    return ucl_string_create(strdup("Hello, world!"));
-}
-
 LISP_FUNC_1(ucl_builtin_type, arg) {
     switch (arg->type) {
         case UCL_TYPE_CELL:
diff --git a/src/builtins.h b/src/builtins.h
index fe2ce5e..a1e8908 100644
--- a/src/builtins.h
+++ b/src/builtins.h
@@ -46,7 +46,6 @@
     static struct ucl_object *func_name##_impl(struct ucl_object *arg0_name, struct ucl_object *arg1_name)
 
 
-struct ucl_object *ucl_builtin_hello_world(struct ucl_object *args);
 struct ucl_object *ucl_builtin_error(struct ucl_object *args);
 struct ucl_object *ucl_builtin_type(struct ucl_object *args);
 struct ucl_object *ucl_builtin_symbol_p(struct ucl_object *args);
diff --git a/src/main.c b/src/main.c
index 385d5fe..ad3c32b 100644
--- a/src/main.c
+++ b/src/main.c
@@ -17,13 +17,32 @@ int main(int argc, const char **argv) {
     ucl_state_put(state, "/", ucl_builtin_create(ucl_builtin_div));
     ucl_state_put(state, "%", ucl_builtin_create(ucl_builtin_mod));
 
+    ucl_state_put(state, "concat", ucl_builtin_create(ucl_builtin_concat));
+
+    ucl_state_put(state, "error", ucl_builtin_create(ucl_builtin_error));
+    ucl_state_put(state, "type", ucl_builtin_create(ucl_builtin_type));
+    ucl_state_put(state, "symbol-p", ucl_builtin_create(ucl_builtin_symbol_p));
+    ucl_state_put(state, "string-p", ucl_builtin_create(ucl_builtin_string_p));
+    ucl_state_put(state, "int-p", ucl_builtin_create(ucl_builtin_int_p));
+    ucl_state_put(state, "list-p", ucl_builtin_create(ucl_builtin_list_p));
+
     struct ucl_object *sexp = ucl_parse(argv[1]);
     struct ucl_object *result = ucl_evaluate(state, ucl_car(sexp));
 
-    assert(result != NULL);
-    assert(result->type == UCL_TYPE_INT);
-
-    printf("%d\n", result->integer);
+    switch (result->type) {
+        case UCL_TYPE_INT:
+            printf("%d\n", result->integer);
+            break;
+        case UCL_TYPE_STRING:
+            printf("\"%s\"\n", result->string);
+            break;
+        case UCL_TYPE_SYMBOL:
+            printf("%s\n", result->string);
+            break;
+        case UCL_TYPE_ERROR:
+            printf("ERROR: %s\n", result->error);
+            return 1;
+    }
 
     return 0;
 }