Using `undefined?` for anything other than JS interop is not recommended. I
don't see any issues with:
(def foo (atom ::uninitialized))
For your watcher case.
On Mon, Jan 14, 2013 at 11:25 PM, Frank Siebenlist <
frank.siebenl...@gmail.com> wrote:
> Ok - ClojureScript has an undefined? function that works like:
>
>
> ClojureScript:cljs.user> (def v)
>
> ClojureScript:cljs.user> (undefined? v)
> true
> ClojureScript:cljs.user> (def w nil)
> nil
> ClojureScript:cljs.user> (undefined? w)
> false
> ClojureScript:cljs.user> (defn f [v] (if (undefined? v) :no-value v))
> #<function f(v){
> if((void 0 === v))
> {return "\uFDD0:no-value";
> } else
> {return v;
> }
> }>
> ClojureScript:cljs.user> (f z)
> :no-value
> ClojureScript:cljs.user> (f 1)
> 1
> ClojureScript:cljs.user> (f y)
> nil
>
>
> which indicates that I can use that scheme to pass and detect "no-value"
> arguments in cljs.
>
> Isn't it great to answer your own Qs ;-)
>
> -FS.
>
>
>
> On Jan 14, 2013, at 7:47 PM, Frank Siebenlist <frank.siebenl...@gmail.com>
> wrote:
>
> > For clojure I came up with the following alternative using an unbound
> var:
> >
> > user=> (def v)
> > #'user/v
> > user=> (defn f [x] (if (var? x) (if (bound? x) x :no-value) x))
> > #'user/f
> > user=> (f v)
> > #<Unbound Unbound: #'user/v>
> > user=> (f #'v)
> > :no-value
> > user=> (f #'map)
> > #'clojure.core/map
> > user=> (type (f v))
> > clojure.lang.Var$Unbound
> > user=>
> >
> > which would indicate that I could pass an unbound var as the argument to
> indicate a "no-value" value, which I can either detect thru the type or the
> bound? test.
> >
> > However, next issue is how to do this in ClojureScript as we do not have
> any vars and therefor no unbound vars…?
> >
> > -FS.
> >
> >
> > On Jan 14, 2013, at 7:07 PM, Frank Siebenlist <
> frank.siebenl...@gmail.com> wrote:
> >
> >> Understood.
> >>
> >> … but shouldn't it be a standardized constant for the whole community
> to use to avoid any interoperability issues and many reinvented wheels?
> >>
> >> The concept of no-value versus nil is a pretty basic one - there must
> be better solutions (re)invented many times over ;-)
> >>
> >> -FS.
> >>
> >>
> >> On Jan 14, 2013, at 5:23 PM, Timothy Baldridge <tbaldri...@gmail.com>
> wrote:
> >>
> >>> It's fairly common in situations like this to use a namespaced
> keyword. For instance ::unknown (which is short for my.namespace/unknown).
> >>>
> >>>
> >>> On Mon, Jan 14, 2013 at 6:06 PM, Frank Siebenlist <
> frank.siebenl...@gmail.com> wrote:
> >>> I'm using those watcher-fns that get called when the watched ref
> changes, and the watcher-fn gets passed the old-value and the new-value.
> >>>
> >>> Now, nil is a proper value for a key-value and well as a val-value in
> a map, so passing nil does not give you the info whether or not an
> old-value existed or not, or whether a new-value is nil or no-value.
> >>>
> >>> With the getter fn: (get m k no-value-here), you have the option to
> pass this no-value-here argument which gets returned if there was no value
> - this allows you to distinguish nil from "no-value". However, in the
> watcher-fn you cannot pass such a no-value argument.
> >>>
> >>> One possible solution would be to define a well-know URI for the value
> of "no-value" - something like for example: "uri:
> http://clojure.org/uri/no-value";, or some other standardized constant.
> >>>
> >>> Any other/better suggestions?
> >>>
> >>> Thanks, FrankS.
> >>>
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