The special form
behaves computationally as if it is not present (other than to affect the semantics), and is only allowed in certain contexts, such as after the variable list in a
There are two distinct uses of
: one is to declare Lisp variables as "special" (this affects the semantics of the appropriate bindings of the variables), and the other is to provide advice to help the Common Lisp system (in reality the compiler) run your Lisp code faster, or with more sophisticated debugging options.
lambda-listspecifies the value to be returned when a programmer asks for the arglist of a function
valuesspecifies the value to be returned when you ask for a description of the results of a function
invisible-framespecifies that calls to this function should not appear in a debugger backtrace
aliasspecifies that calls to this function should be displayed as calls to an alternative function in a debugger backtrace
If you use
to specify types (and so turn off type-checking for the specified symbols) and then supply the wrong type, you may obtain a "Segmentation Violation". You can check this by interpreting the code (rather than compiling it).