15.4.9.6 Deviations from Standard Modula-2
A few changes have been made to make Modula-2 programs easier to debug.
This is done primarily via loosening its type strictness:
-  Unlike in standard Modula-2, pointer constants can be formed by
integers.  This allows you to modify pointer variables during
debugging.  (In standard Modula-2, the actual address contained in a
pointer variable is hidden from you; it can only be modified
through direct assignment to another pointer variable or expression that
returned a pointer.)
-  C escape sequences can be used in strings and characters to represent
non-printable characters.  GDB prints out strings with these
escape sequences embedded.  Single non-printable characters are
printed using the ‘CHR(nnn)’ format.
-  The assignment operator (:=) returns the value of its right-hand
argument.
-  All built-in procedures both modify and return their argument.