Hello.
Perl 5.32 (year 2020) introduced a new ability of binary comparison operators. Now they can be chained! ( https://perldoc.perl.org/5.32.0/perldelta#Chained-comparisons-capability ).
And perldoc describes this new usage in:
* https://perldoc.perl.org/perlop#Operator-Precedence-and-Associativity
* https://perldoc.perl.org/perlop#Relational-Operators
* https://perldoc.perl.org/perlop#Equality-Operators

There are some short-circuiting operators in Perl from before 5.32 version: &&, ||, //, and, or (not xor).

What is difference between associativity and chainity?
I suggest to distinguish these two attributes of operators as follows: associativity only sets a direction of operations; chainity sets an ability to 'communicate' between consecutive operators, in other words - a later operator can influence the behaviour of a former operator.

Then I suggest to improve a table of Perl operators by introducing two more columns: chainity (ability to chain) and ability to short-circuit.
This will help to newcomers and beginners! I have often used these tables of operators from perlcheat and from beginning of the perlop:https://perldoc.perl.org/perlop#Operator-Precedence-and-Associativity, because it takes time to remember precedence and direction of associativity. Two new attributes in the table will be more usable than a searching of them through the whole long perlop document.
In the current table of attributes I find only one column, which contains values: nonassoc, left, right, chained, chain/na. Chained implies associativity, but it lefts its direction undefined, e.g. in the line: "chained     < > <= >= lt gt le ge" newcomer doesn't know direction. We know - it is left-assoc.

Perl is difficult to memorize and it has long learning curve because of its archaity and many many rules with many exceptions, which makes a life easier, but makes learning/memorizing - difficult. So tables/cheatsheets are useful to have near a hand. E.g. operators 'or' and 'xor' seem similar by their appearance and by their category (both are logical operators), but one has an ability to short-circuit and another - hasn't. This was a surprise for me. Upd.The surprise was not about short-circuit, but about returning last evaluated value.

I can't test a new perl 5.32 now (upd. perlbrew isn't working /upd.*, and there are no online IDEs where I could find a new version: all use older versions, including WebPerl:https://webperl.zero-g.net/democode/index.html which uses 5.28).
But I hope that I will be correct when talking further about new abilities of comparison operators.

So, first of all I guess that new version outputs different results for these two lines of codes:
2 < 4 < 3 and ( 2 < 4 ) < 3. In the first example the chaining of operators occurs and in the second example - ordinary comparisons occurs. First outputs - 0/'', second - 1. Am I wrong? Here parentheses cut a chain of operators: one operator doesn't see another. If second behaves same as first then it would be backwards incompatible.

Only some examples of chained comparisons: "1 < 3 <= 3 > 0 le 1 gt 0 ---> 1", "1 < 2 < ... < 9 ---> 1", "1 ne 2 ne 1 ---> 1".

How can we describe a behaviour of chained comparison operators?
I suggest the following way. If an operator "sees" another operator towards the direction of associativity (i.e. it is chained to it), then it changes it behaviour (btw. becomes overloaded) - it compares both operands and in case of TRUE returns right operand (once evaluated), and in case of FALSE - returns 0/''. This description allows the last operator to be not chained, so it will behave as usual comparison op (TRUE - 1, FALSE - 0/'').

Chainity implies (requires) associativity, as ability to short-circuit does, but chaining does not imply an ability to short-circuit and vice versa, so I suggest to keep these two attributes separately. Maybe in a future perl such will occur.
By the way, operators  &&, ||, //, and, or are short-circuiting, but they are not chained (i.e. we can put parentheses in left-assoc pattern to "blind" consecutive operators and result will not change).

Also I have an idea (I don't believe that it is good, but I leave it here if someone wants to discuss). That: writer could choose by himself if he wants his operator to look to the next operator (i.e. to make a chain). One way could be to prepend '&' before an operator. So then $A &< $B &> $C < $D should work as a chain (note no '&' at the last operator).

Once more about tables. From perlop it is unknown which 'equality' operators can be chained and which can not. This needs a clarification.


Here I'll leave some links to older topics (by me), which can be somehow related to this one:
Pls more operators, e.g. <&&=
'xor' operator is not a sibling to 'or' and 'and'?


UPDATE:
Here is my suggestion of an expanded table (which is a bit incomplete, but I want to show an idea). Note that vertical lines mean that some operators are the same precedence but divided into separate lines:

  ASSOC.     COND. SHORT-C. CHAINS  OP.
  left                              terms and list operators (leftward
+)
  left                              ->
  nonassoc                          ++ --
  right                             **
  right                             ! ~ \ and unary + and -
  left                              =~ !~
  left                              * / % x
  left                              + - .
  left                              << >>
  nonassoc                          named unary operators
  LEFT       no    yes      yes     < > <= >= lt gt le ge
| LEFT       no    yes      yes     == != eq ne ~~
| LEFT       no    no       no      <=> cmp
  nonassoc                          isa
  left                              &
  left                              | ^
  left       yes   yes      no      &&
  left       yes   yes      no      || //
  nonassoc                          ..  ...
  right      yes   no       no      ?:
  right                             = += -= *= etc. goto last next red
+o dump
  left                              , =>
  nonassoc                          list operators (rightward)
  right                             not
  left       yes   yes      no      and
| left       yes   yes      no      or
| left       no    no       no      xor
[download]

Upd. Also created a documentation issue asking to expand this table of attributes -- https://github.com/Perl/perl5/issues/18574.

(*upd. perlbrew failed to install from its download page, but later I found it in Software manager and installed.)

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