Summary of Termination Test Clauses (ANSI and GNU Common Lisp Document)

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#### 6.1.1.10 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 Termination Test Clauses.