Editing Relational operator (section)

===Operator chaining===
In mathematics, it is common practice to chain relational operators, such as in 3 < x < y < 20 (meaning 3 < x ''and'' x < y ''and'' y < 20). The syntax is clear since these relational operators in mathematics are transitive.

However, many recent programming languages would see an expression like 3 < x < y as consisting of two left (or right-) associative operators, interpreting it as something like <code>(3 < x) < y</code>. If we say that x=4, we then get <code>(3 < 4) < y</code>, and evaluation will give <code>true < y</code> which generally does not make sense. However, it does compile in C/C++ and some other languages, yielding surprising result (as ''true'' would be represented by the number 1 here).

It is possible to give the expression <code>x < y < z</code> its familiar mathematical meaning, and some programming languages such as Python and [[Raku (programming language)|Raku]] do that. Others, such as C# and Java, do not, partly because it would differ from the way most other infix operators work in C-like languages. The [[D programming language]] does not do that since it maintains some compatibility with C, and "Allowing C expressions but with subtly different semantics (albeit arguably in the right direction) would add more confusion than convenience".<ref>{{cite book |last=Alexandrescu |first=Andrei |title=The D Programming Language |year=2010 |publisher=Addison Wesley |page=58 |isbn=978-0-321-63536-5}}</ref>

Some languages, like [[Common Lisp]], use multiple argument predicates for this. In Lisp <code>(<= 1 x 10)</code> is true when x is between 1 and 10.