Short-circuit evaluation

Short-circuit evaluation, minimal evaluation, or McCarthy evaluation (after <a href="/facts/John_McCarthy_(computer_scientist)/ajKU4SdD">John McCarthy</a>) is the semantics of some <a href="/facts/Logical_connective/VkPhUs6M">Boolean operators</a> in some <a href="/facts/Programming_language/cWTYbgWa">programming languages</a> in which the second argument is executed or evaluated only if the first argument does not suffice to determine the value of the expression: when the first argument of the AND function evaluates to false, the overall value must be false; and when the first argument of the OR function evaluates to true, the overall value must be true.
In programming languages with <a href="/facts/Lazy_evaluation/mD3DxDkc">lazy evaluation</a> (<a href="/facts/Lisp_(programming_language)/xJHA3CrX">Lisp</a>, <a href="/facts/Perl/fx31kjlT">Perl</a>, <a href="/facts/Haskell/ydEsHuGy">Haskell</a>), the usual <a href="/facts/Boolean_expression/qWS7Ef6n">Boolean operators</a> short-circuit. In others (<a href="/facts/Ada_(programming_language)/Y2yHel4l">Ada</a>, <a href="/facts/Java_(programming_language)/9ScgFyAL">Java</a>, <a href="/facts/Delphi_(software)/sUFUXQ8r">Delphi</a>), both short-circuit and standard Boolean operators are available. For some Boolean operations, like <a href="/facts/Exclusive_or/FHyr7hGQ">exclusive or</a> (XOR), it is impossible to short-circuit, because both operands are always needed to determine a result.
Short-circuit operators are, in effect, <a href="/facts/Control_structure/2XTDfErC">control structures</a> rather than simple arithmetic operators, as they are not <a href="/facts/Strict_function/Fc6PYymI">strict</a>. In <a href="/facts/Imperative_language/6b5dUnE1">imperative language</a> terms (notably <a href="/facts/C_(programming_language)/Ky2No763">C</a> and <a href="/facts/C%2B%2B/Et0F2qn9">C++</a>), where side effects are important, short-circuit operators introduce a <a href="/facts/Sequence_point/f4xdSEAx">sequence point</a>: they completely evaluate the first argument, including any <a href="/facts/Side_effect_(computer_science)/AU3GlLzG">side effects</a>, before (optionally) processing the second argument. <a href="/facts/ALGOL_68/NTnc9fy7">ALGOL 68</a> used proceduring to achieve user-defined short-circuit operators and procedures.
The use of short-circuit operators has been criticized as problematic:

<blockquote>The conditional connectives — "cand" and "cor" for short — are ... less innocent than they might seem at first sight. For instance, cor does not distribute over cand: compare
(A cand B) cor C with (A cor C) cand (B cor C);
in the case ¬A ∧ C , the second expression requires B to be defined, the first one does not. Because the conditional connectives thus complicate the formal reasoning about programs, they are better avoided.— <a href="/facts/Edsger_W._Dijkstra/910x0MjT">Edsger W. Dijkstra</a></blockquote>

Short-circuit evaluation open-in-new

Short-circuit evaluation