Re: Interval Comparisons

On 04/06/2024 09:14, Lawrence D'Oliveiro wrote:

Would it break backward compatibility for C to add a feature like this
from Python? Namely, the ability to check if a value lies in an interval:
      def valid_char(c) :
         "is integer c the code for a valid Unicode character." \
         " This excludes surrogates."
         return \
             (
                 0 <= c <= 0x10FFFF
             and
                 not (0xD800 <= c < 0xE000)
             )
     #end valid_char

Do you mean, could C treat "a <= x <= b" as "(a <= x) && (x <= b)" without breaking existing code?  The answer is no, C treats it as the expression "(a <= x) <= b".  So you would be changing the meaning of existing C code.  I think it's fair to say there is likely to be very little existing correct and working C code that relies on the current interpretation of such expressions, but the possibility is enough to rule out such a change ever happening in C.  (And it would also complicate the grammar a fair bit.)
<https://c-faq.com/expr/transitivity.html>