when you say the word "false" I'm assuming you're referring to "false?" the
function (not "false" the boolean value), otherwise I don't understand
so like: "What matters is that *false?* returns truthy values when called
with any members of []"
makes sense to me.
So all I was saying above is that it should throw when [] is empty just as
it does when [] is not empty, but it doesn't throw when empty because it's
never called (by "it" i mean "false" not "false?")
=> (type false)
java.lang.Boolean
=> (type false?)
clojure.core$false_QMARK_
=> (fn? false)
false
=> (fn? false?)
true
But really, if you were not talking about "false?" then I don't get it (??)
On Thu, May 23, 2013 at 4:48 PM, Michał Marczyk <michal.marc...@gmail.com>wrote:
> Whether (false 1) or (false true) is truthy is irrelevant. What
> matters is that false returns truthy values when called with any
> members of [], which is of course the case, as [] has no members. (For
> it not to be the case, there would have to exist an x in [] for which
> (false x) were not truthy -- clearly there is no such x.)
>
> This is the same story as with quantification restricted to the empty set:
>
> \forall x \in \emptyset . \phi(x)
>
> is true regardless of what \phi is, and intimately related to how
> implication works in classical logic (since the above is shorthand for
> a formula involving implication):
>
> x -> y
>
> is true when x is false, regardless of what value y takes. (It's also
> true when y is true, regardless of what value x takes; this, however,
> is not relevant here.)
>
> Cheers,
> M.
>
>
> On 23 May 2013 06:31, atkaaz <atk...@gmail.com> wrote:
> > Well, seems to me more like this:
> > if [] is empty then return true
> > otherwise check (pred everyx in coll)
> > however this allows for any pred especially(in this case) invalid preds:
> > `false` is not a function/pred
> > => (false 1)
> > ClassCastException java.lang.Boolean cannot be cast to clojure.lang.IFn
> > cgws.notcore/eval2542 (NO_SOURCE_FILE:1)
> > => (false true)
> > ClassCastException java.lang.Boolean cannot be cast to clojure.lang.IFn
> > cgws.notcore/eval2564 (NO_SOURCE_FILE:1)
> >
> > doesn't seem truthy to me
> >
> > Thanks.
> >
> >
> > On Thu, May 23, 2013 at 3:08 AM, Michał Marczyk <
> michal.marc...@gmail.com>
> > wrote:
> >>
> >> On 22 May 2013 18:34, atkaaz <atk...@gmail.com> wrote:
> >> > I think the exception is thrown because you basically called (every?
> >> > false
> >> > coll) however on my clojure version I cannot reproduce it oh wait
> there
> >> > we
> >> > go, some bug here with empty collection (maybe someone can pick it
> up):
> >> > => (every? false [1 2 3])
> >> > ClassCastException java.lang.Boolean cannot be cast to
> clojure.lang.IFn
> >> > clojure.core/every? (core.clj:2423)
> >> > => (every? false [])
> >> > true
> >> >
> >> > => *clojure-version*
> >> > {:interim true, :major 1, :minor 6, :incremental 0, :qualifier
> "master"}
> >>
> >> (every? false []) should return true if and only if (false x) is
> >> truthy for every x in [], which is certainly the case.
> >>
> >> Cheers,
> >> Michał
> >>
> >>
> >> >
> >> >
> >> >
> >> >
> >> >
> >> > On Wed, May 22, 2013 at 7:17 PM, Peter Mancini <
> peter.manc...@gmail.com>
> >> > wrote:
> >> >>
> >> >> So I did some coding and came up with this but it is broken;
> >> >>
> >> >> (= java.lang.Boolean (type false)) ;;evaluates to true
> >> >>
> >> >> (defn all-true?
> >> >> [coll]
> >> >> (every? (cond (= java.lang.Boolean (type identity)) identity :else
> >> >> false) coll)) ;;compiles
> >> >>
> >> >> (all-true? '(true true true)) ;; throws
> java.lang.ClassCastException:
> >> >> java.lang.Boolean cannot be cast to clojure.lang.IFn
> >> >> (all-true? '(true true false))
> >> >> (all-true? '(true true 3))
> >> >>
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