cond

Cond is a term used to denote a conditional construct in programming languages and logic. In Lisp family languages, cond is a built-in multi-branch conditional that selects among several possibilities based on tested conditions.

In Common Lisp and related dialects, a cond expression consists of a sequence of clauses. Each clause is a list whose first element is a test expression and whose remaining elements are forms to evaluate if the test is true. The first clause whose test evaluates to true is executed, and its results are returned. If no clause matches, the value is nil or an error is implementation-defined; a final clause with a test of t (or an else clause in Scheme) provides a default case.

Example in Scheme or Common Lisp: (cond ((< x 0) 'negative) ((= x 0) 'zero) (else 'positive)). This evaluates to 'negative, 'zero, or 'positive depending on x.

Outside Lisp, cond is not a universal keyword, but the term remains a descriptive shorthand for conditional forms. Other languages offer similar branching constructs, such as if-else, switch/case, or pattern matching.

See also: conditional expression, Lisp, Scheme, Emacs Lisp.