Common Lisp Unbound-Variable error?

Question

I'm using the CLOS and I'm trying to write a function called def-concept that uses defclass to create a subclass of the class Concept. When I pass in a command like (def-concept Car), I get an error saying "Attempt to take the value of the unbound variable `car'. Why is this happening? Is there a way to "dereference" a variable from a list of arguments?

Answer 1

You can't write a /function/ called DEF-CONCEPT that does that; when you evaluate (DEF-CONCEPT CAR), the first thing Lisp does is try to get the variable-value of CAR ... hence the error. You have to either call it as (DEF-CONCEPT 'CAR) [note the quote], or (more likely what you want here) make DEF-CONCEPT a macro.



In the former case, you can't use DEFCLASS -- use the MOP function ENSURE-CLASS to programmatically create a class. In the latter case, your macro can expand into a DEFCLASS form.

Answer 2

Yes you can deference a variable from a list of argument by first declaring the variable function.

Answer 3

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Answer 4

try quasi-quoting or sharp-quoting.