为什么可以引用 KEYWORD 包中以前未定义的变量？
Why is it possible to refer to a previously undefined variable in the KEYWORD package?
引用之前未定义的变量将导致错误：The variable X is unbound（SBCL 的错误消息）。但是，引用 KEYWORD 包中先前未定义的变量不会导致任何错误。例如，KEYWORD:XYZ 神奇地具有 :XYZ 的值，即使用户之前没有定义和导出该变量。为什么会这样？怎么可能即时自动创建一个变量？
Lisp reader 实习生以 package marker in the KEYWORD package; the package marker is a colon by default. Symbols interned in the KEYWORD package are automatically made external. From 11.1.2.3.1 of the HyperSpec:
开头的符号
The KEYWORD package is treated differently than other packages in that special actions are taken when a symbol is interned in it. In particular, when a symbol is interned in the KEYWORD package, it is automatically made to be an external symbol and is automatically made to be a constant variable with itself as a value.
引用之前未定义的变量将导致错误：The variable X is unbound（SBCL 的错误消息）。但是，引用 KEYWORD 包中先前未定义的变量不会导致任何错误。例如，KEYWORD:XYZ 神奇地具有 :XYZ 的值，即使用户之前没有定义和导出该变量。为什么会这样？怎么可能即时自动创建一个变量？
Lisp reader 实习生以 package marker in the KEYWORD package; the package marker is a colon by default. Symbols interned in the KEYWORD package are automatically made external. From 11.1.2.3.1 of the HyperSpec:
The KEYWORD package is treated differently than other packages in that special actions are taken when a symbol is interned in it. In particular, when a symbol is interned in the KEYWORD package, it is automatically made to be an external symbol and is automatically made to be a constant variable with itself as a value.