It's very common for a sequence argument to also work with nil, with the
same semantics as an empty sequence. They are completely different things
but
Clojure is sloppy in this regard.
I believe this is intended.
Thanks,
Ambrose
On Tue, Apr 8, 2014 at 2:08 PM, Jeff Mad <jeff...@gmail.com> wrote:
> Hi,
> I am new to Clojure, so please forgive me if this does not make sense.
>
> I was surprised to find out in the REPL that every? returns true if you
> pass in an empty or nil collection.
>
> user=> (every? #(= 77 %) nil)
>
> true
>
> user=> (every? #(= 77 %) '())
>
> true
>
>
> I looked at the source for every? and it made sense to me why this
> happens given that every? is recursive and the termination condition is
> when coll runs out of items to process.
>
> Would it make more sense to define every? with a loop, or is the caller
> expected to know better than to call it with nil?
>
> Thanks,
>
> --jeff
>
>
> (defn every2?
>
> "Returns true if (pred x) is logical true for every x in coll, else
>
> false."
>
> {:tag Boolean
>
> :added "1.0"
>
> :static true}
>
> [pred coll]
>
> (if (empty? coll)
>
> false
>
> (loop [c coll]
>
> (cond
>
> (nil? (seq c)) true
>
> (pred (first c)) (recur (next c))
>
> :else false))))
>
>
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