+ vm = SCM_VM_DATA (x);
+
+ scm_puts ("#<vm ", port);
+ switch (vm->engine)
+ {
+ case SCM_VM_REGULAR_ENGINE:
+ scm_puts ("regular-engine ", port);
+ break;
+
+ case SCM_VM_DEBUG_ENGINE:
+ scm_puts ("debug-engine ", port);
+ break;
+
+ default:
+ scm_puts ("unknown-engine ", port);
+ }
+ scm_uintprint (SCM_UNPACK (x), 16, port);
+ scm_puts (">", port);
+}
+
+\f
+/*
+ * VM Error Handling
+ */
+
+static void vm_error (const char *msg, SCM arg) SCM_NORETURN;
+static void vm_error_bad_instruction (scm_t_uint32 inst) SCM_NORETURN;
+static void vm_error_unbound (SCM proc, SCM sym) SCM_NORETURN;
+static void vm_error_unbound_fluid (SCM proc, SCM fluid) SCM_NORETURN;
+static void vm_error_not_a_variable (const char *func_name, SCM x) SCM_NORETURN;
+static void vm_error_not_a_thunk (const char *func_name, SCM x) SCM_NORETURN;
+static void vm_error_apply_to_non_list (SCM x) SCM_NORETURN;
+static void vm_error_kwargs_length_not_even (SCM proc) SCM_NORETURN;
+static void vm_error_kwargs_invalid_keyword (SCM proc, SCM obj) SCM_NORETURN;
+static void vm_error_kwargs_unrecognized_keyword (SCM proc, SCM kw) SCM_NORETURN;
+static void vm_error_too_many_args (int nargs) SCM_NORETURN;
+static void vm_error_wrong_num_args (SCM proc) SCM_NORETURN;
+static void vm_error_wrong_type_apply (SCM proc) SCM_NORETURN;
+static void vm_error_stack_overflow (struct scm_vm *vp) SCM_NORETURN;
+static void vm_error_stack_underflow (void) SCM_NORETURN;
+static void vm_error_improper_list (SCM x) SCM_NORETURN;
+static void vm_error_not_a_pair (const char *subr, SCM x) SCM_NORETURN;
+static void vm_error_not_a_bytevector (const char *subr, SCM x) SCM_NORETURN;
+static void vm_error_not_a_struct (const char *subr, SCM x) SCM_NORETURN;
+static void vm_error_no_values (void) SCM_NORETURN;
+static void vm_error_not_enough_values (void) SCM_NORETURN;
+static void vm_error_continuation_not_rewindable (SCM cont) SCM_NORETURN;
+static void vm_error_bad_wide_string_length (size_t len) SCM_NORETURN;
+#if VM_CHECK_IP
+static void vm_error_invalid_address (void) SCM_NORETURN;
+#endif
+#if VM_CHECK_OBJECT
+static void vm_error_object (void) SCM_NORETURN;
+#endif
+#if VM_CHECK_FREE_VARIABLES
+static void vm_error_free_variable (void) SCM_NORETURN;
+#endif
+
+static void
+vm_error (const char *msg, SCM arg)