My read of the spec is that either behaviour is allowable.

DEFSTRUCT[1] says:

"If a slot is not initialized in this way, it is initialized by evaluating slot-initform in the slot description at the time the constructor function is called."

Which makes no reference to the environment in which the form should be evaluated in.

Later on it says:

"It is as if the slot-initforms were used as initialization forms for the keyword parameters of the constructor function"

The page describing keyword arguments in ordinary lambda lists[2] also makes no reference to which environment should be used for initforms.

I guess they didn't think about people using closures for initforms when they were drawing it up?

To side-step the issue I would invoke a closure from the initform instead (if that's how you want to do it).

[1] http://www.lispworks.com/documentation/HyperSpec/Body/m_defstr.htm
[2] http://www.lispworks.com/documentation/HyperSpec/Body/03_dad.htm

On 03/08/15 23:04, Peter Stirling wrote:

That makes no sense, the bindings in the let are independent.

On 03/08/15 22:42, Laughing Water wrote:

It looks like you need a LET* to guarantee the order of evaluation within your LET. Otherwise, it’s undefined.

Laughing Water

On Aug 3, 2015, at 3:27 PM, Jean-Claude Beaudoin <jean.claude.beaudoin@gmail.com> wrote:

Please consider the following code:

(defparameter init-a 1)

(let ((init-a 42) (serial-no 0))
(defstruct foo (a init-a) (b (incf serial-no)))
(defun get-foo-serial-no () serial-no))

(defstruct (bar (:include foo)) (c 33) d)

When one loads the above and then try to call #'make-bar the result
varies widely from one lisp implementation (clisp) to another.

clisp: (make-bar) --> #S(BAR :A 1 :B 1 :C 33 :D NIL)
ccl: (make-bar) --> <enter the debugger saying: "Unbound variable: SERIAL-NO">

lispworks, allegro and sbcl also behave more or less like ccl.

What is the proper ANSI-CL behavior in this case here?
Is clisp right in evaluating the slot initform in its "proper" lexical context?
Or is the correct behavior to replicate the slot initform verbatim
in the sub-structure constructor regardless of its original lexical context
like the others do?

I guess that this question has probably been asked before, in a somewhat
distant past, but my google skills have not been sharp enough to find it, sorry.

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