+void midrule_value_at (location loc, char const *format, ...)
+ __attribute__ ((__format__ (__printf__, 2, 3)));
+
+/** A fatal error, causing immediate exit. */
+
+void fatal (char const *format, ...)
+ __attribute__ ((__noreturn__, __format__ (__printf__, 1, 2)));
+
+void fatal_at (location loc, char const *format, ...)
+ __attribute__ ((__noreturn__, __format__ (__printf__, 2, 3)));