The simplest way to execute arbitrary code within a loop body is with a do clause. Compared to the clauses I’ve described so far, with their prepositions and subclauses, do is a model of Yodaesque simplicity.7 A do clause consists of the word do (or doing) followed by one or more Lisp forms that are all evaluated when the clause is. The do clause ends at the closing parenthesis of the loop or the next loop keyword.

Another, more dramatic, form of immediate execution is a return clause. This clause consists of the word return followed by a single Lisp form, which is evaluated, with the resulting value immediately returned as the value of the loop.

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