The do and doing constructs evaluate the supplied forms wherever they occur in the expanded form of loop. The form argument can be any compound form. Each form is evaluated in every iteration. Because every loop clause must begin with a loop keyword, the keyword do is used when no control action other than execution is required.
The return construct takes one form. Any values returned by the form are immediately returned by the loop form. It is equivalent to the clause do (return-from block-name value), where block-name is the name specified in a named clause, or nil if there is no named clause.
188.8.131.52 Examples of unconditional execution