substitute-if

(substitute-if new predicate sequence &key key)

Returns a new sequence in which every element satisfying predicate is replaced by new; all other elements are kept unchanged. It is substitute with the eql comparison replaced by a predicate call, so it takes no :test — the predicate is the test. The optional :key keyword takes a selector function applied to each element before the predicate sees it (the replacement value is new itself, unkeyed). The sequence may be a list, a string or a vector, and the result keeps that kind. The original sequence is not modified; use nsubstitute-if for the destructive version (lists only).