block

(block name body...)

Establishes a named block around body and returns the value of the last form, or the value thrown by a matching (return-from name value) fired during the body's execution. Names are matched on every backend: an inner return-from targeting an outer block passes through intervening blocks and loops, and (block nil ...) additionally catches plain (return ...) like the loop macros' implicit nil block. The match is LEXICAL on every backend — a return-from (or a plain return) inside a closure exits the block that encloses it in the SOURCE, so a handler-bind handler written inside (block nil ...) exits that block, not whichever same-named block is running where the condition was signalled. Exiting a block whose activation has already returned is an error.