Summary of Conditional Execution Clauses (ANSI and GNU Common Lisp Document)

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#### 6.1.1.12 Summary of Conditional Execution Clauses

The `if` and `when` constructs take one form as a test and a clause that is executed when the test yields true. The clause can be a value accumulation, unconditional, or another conditional clause; it can also be any combination of such clauses connected by the loop `and` keyword.

The loop `unless` construct is similar to the loop `when` construct except that it complements the test result.

The loop `else` construct provides an optional component of `if`, `when`, and `unless` clauses that is executed when an `if` or `when` test yields false or when an `unless` test yields true. The component is one of the clauses described under `if`.

The loop `end` construct provides an optional component to mark the end of a conditional clause.

For more information, see Conditional Execution Clauses.