On Mon, Aug 3, 2015 at 10:12 PM, Peter Stirling peter@pjstirling.plus.com wrote:
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 byevaluating *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*http://www.lispworks.com/documentation/HyperSpec/Body/26_glo_i.htm#initialization_form for the *keyword parameters* http://www.lispworks.com/documentation/HyperSpec/Body/26_glo_k.htm#keyword_parameter of the constructor function"
Later later on it says:
"The slot default init forms are evaluated in the lexical environment in which the defstruct form itself appears and in the dynamic environment in which the call to the constructor function appears."
So the defstruct sees the local/lexical serial-no but a call to make-bar outside does not.
In between we get more clues: "The symbols which name the slots must not be used by the implementation as the names for the lambda variables in the constructor function, since one or more of thosesymbols might have been proclaimed special or might be defined as the name of a constant variable. "
Indeed, if one compiles the example provided, when one *compiles *(ACL has both an interpreter and compiler, and they vary) make-bar one learns:
Warning: Free reference to undeclared variable serial-no assumed special.
I checked the spec on included structs but did not notice anything about included slot init-form evaluation, but I guess it makes sense that included slots be assembled and evaluated as if coded with the including struct.
-hk
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 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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