ANSI Common Lisp 4 Types and Classes 4.4 Dictionary of Types and Classes
The type boolean contains the symbols t and nil,
which represent true and false, respectively.
- See Also:
t (constant variable),
nil (constant variable),
Conditional operations, such as if,
permit the use of generalized booleans,
not just booleans;
any non-nil value,
not just t,
counts as true for a generalized boolean.
However, as a matter of convention,
the symbol t is considered the canonical value to use
even for a generalized boolean when no better choice presents itself.
- Allegro CL Implementation Details: