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6.1.1.5.3 Summary of Termination Test Clauses

The for and as constructs provide a termination test that is determined by the iteration control clause.

The repeat construct causes termination after a specified number of iterations. (It uses an internal variable to keep track of the number of iterations.)

The while construct takes one form, a test, and terminates the iteration if the test evaluates to false. A while clause is equivalent to the expression (if (not test) (loop-finish)).

The until construct is the inverse of while; it terminates the iteration if the test evaluates to any non-nil value. An until clause is equivalent to the expression (if test (loop-finish)).

The always construct takes one form and terminates the loop if the form ever evaluates to false; in this case, the loop form returns nil. Otherwise, it provides a default return value of t.

The never construct takes one form and terminates the loop if the form ever evaluates to true; in this case, the loop form returns nil. Otherwise, it provides a default return value of t.

The thereis construct takes one form and terminates the loop if the form ever evaluates to a non-nil object; in this case, the loop form returns that object. Otherwise, it provides a default return value of nil.

If multiple termination test clauses are specified, the loop form terminates if any are satisfied.

For more information, see Section 6.1.4 (Termination Test Clauses).


The following X3J13 cleanup issue, not part of the specification, applies to this section:


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