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The Loop Facility provides the ‘named’ construct to name a loop so that the
Common Lisp special form return-from can be used.
The loop keywords ‘initially’ and ‘finally’ designate loop constructs that cause expressions to be evaluated before and after the loop body, respectively.
The code for any ‘initially’ clauses is collected into one progn in the order
in which the clauses appeared in the loop. The collected code is executed once
in the loop prologue after any implicit variable initializations.
The code for any ‘finally’ clauses is collected into one progn in the order
in which the clauses appeared in the loop. The collected code is executed once
in the loop epilogue before any implicit values are returned from the
accumulation clauses. Explicit returns in the loop body, however, will exit
the loop without executing the epilogue code.