15.25.3.3 Loop Syntax

The following syntax description provides an overview of the syntax for loop clauses.¹⁶

A loop consists of the following types of clauses:

initial-final ::= initially | finally
variables ::= with | initial-final | for-as | repeat
main ::= unconditional | accumulation | conditional | termination | initial-final
loop ::= (loop [named name] {variables}* {main}*)

Note that a loop must have at least one clause; however, for backward compatibility, the following format is also supported:

(loop {tag | expr}*)

where ‘expr’ is any Common Lisp expression that can be evaluated, and ‘tag’ is any symbol not identifiable as a loop keyword. Such a format is roughly equivalent to the following one:

(loop do {tag | expr}*)

A loop prologue consists of any automatic variable initializations prescribed by the variable clauses, along with any initially clauses in the order they appear in the source.

A loop epilogue consists of finally clauses, if any, along with any implicit return value from an accumulation clause or an end-test clause.