Re: Type BOOLEAN

Edi Weitz wrote:
> then current CLSQL will raise an error because the result of FIND is
> most likely neither T nor NIL. I think it's more Lisp-y to allow for
> generalized booleans in this case. It's just that the docs should make
> clear that reloading these instances from the SQL database will give
> you T or NIL and nothing else.

Well, it depends upon how you define "Lisp-y". I've wrestled a bit
with the slot type representing an actual Lisp type versus representing a
SQL data type.

> Any objections?

To the degree, that "declaration are assertations", it's not okay to
lie to Lisp. This is implementation specific, of course. OpenMCL, for
example, computes a slot named ccl:type-predicate for each
effective-slot-definition. It uses this predicate to check values
stored with (setf slot-value-using-class).

As an example:

[email protected]:~> openmcl
Welcome to OpenMCL Version (Beta: Linux) 0.14.2!
? (defclass foo () ((a :initarg :a :type boolean)))

? (make-instance 'foo :a (find 'b '(a b c)))
> Error in process listener(1): The value B, derived from the initarg
  :A, can not be used to set the value of the slot A in #<FOO
  #x354C6DA6>, because it is not of type (OR NULL BOOLEAN). 
> While executing: CCL::%SHARED-INITIALIZE

I have arranged a hook in sql/metaclasses.lisp named
compute-lisp-type-from-slot-specification where it's possible to
change the actual lisp type for a :type attribute in a slot. So, it is
possible to have ":type boolean" actually translate to lisp as ":type
t". While possible, I've tried to stick as much to Lisp semantics as
possible such that:
  (typep slot-value slot-type) => t

As stated, I've thought about this issue and I'll be glad to discuss
it further. 

Kevin







> Cheers,
> Edi.
> 

> +++ oodml.lisp	2004-06-09 01:29:01.000000000 +0200
> @@ -142,7 +142,8 @@ (defun check-slot-type (slotdef val)
>    (let* ((slot-type (specified-type slotdef))
>           (basetype (if (listp slot-type) (car slot-type) slot-type)))
>      (when (and slot-type val)
> -      (unless (typep val basetype)
> +      (unless (or (eq basetype 'boolean)
> +                  (typep val basetype))
>          (error 'sql-user-error
>  	       :message
>  	       (format nil "Invalid value ~A in slot ~A, not of type ~A."

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-- 
Kevin Rosenberg
kevin-HJRc7zDS/[email protected]