On Thu, Nov 5, 2009 at 3:53 PM, Meikel Brandmeyer wrote:
> Hi,
>
> Am 03.11.2009 um 22:41 schrieb jan:
>
> > (defn for-each [f items]
> > (when-not (empty? items)
> > (f (first items))
> > (recur f (rest items
>
> And to not defeat the learning exercise...
>
> (defn for-each
>
Hi,
Am 03.11.2009 um 22:41 schrieb jan:
> (defn for-each [f items]
> (when-not (empty? items)
> (f (first items))
> (recur f (rest items
And to not defeat the learning exercise...
(defn for-each
[f items]
(when-let [s (seq items)]
(f (first s))
(recur f (next s)
I'm working the exercises in SICP using Clojure and learning Clojure as I
go. I've stumbled across a mystifying NullPointerException. I'm implementing
exercise 2.23, where you're supposed to implement a "for-each" method that
takes a function and a list of items. It applies the function to teach it
On Nov 3, 9:41 pm, jan wrote:
> When you only have a single branch in `if' it is more conventional to
> use `when', or in this case `when-not'. And defn sets up a recur point
> so there's no need for the explicit loop either.
I thought "when" was mainly used for side-effects? "if" seems more
app
On Tue, Nov 3, 2009 at 4:22 PM, Brian Hurt wrote:
>
>
> On Tue, Nov 3, 2009 at 4:21 PM, Dean Wampler wrote:
>
>> Ah, of course. Thanks. This works:
>>
>> (defn for-each [f items]
>> (if (not (empty? items))
>> (let [] (f (first items)) (for-each f (rest items)
>>
>>
> Or:
>
> (defn fo
On Tue, Nov 3, 2009 at 4:21 PM, Dean Wampler wrote:
> Ah, of course. Thanks. This works:
>
> (defn for-each [f items]
> (if (not (empty? items))
> (let [] (f (first items)) (for-each f (rest items)
>
>
Or:
(defn for-each [ f items]
> (for-each (fn [x] (println (* x x))) (list 1 2 3
Also Clojure has doseq which defeats the learning exercise but nets a
nicer golf score of 14:
(defn for-each [f items]
(doseq [i items] (f i)))
--~--~-~--~~~---~--~~
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To pos
Brian Hurt writes:
> Of course, you don't have tail call optimization in Clojure (dang jvm). So
> this is probably better:
> (defn for-each [f items]
> (loop [ curr items ]
> (if (empty? curr)
> nil
> (do
> (f (first curr))
> (
Ah, of course. Thanks. This works:
(defn for-each [f items]
(if (not (empty? items))
(let [] (f (first items)) (for-each f (rest items)
(for-each (fn [x] (println (* x x))) (list 1 2 3 4 5))
On Tue, Nov 3, 2009 at 3:13 PM, Kevin Downey wrote:
>
> (f (first items)) => nil
> ((f (fir
(f (first items)) => nil
((f (first items)) (for-each f (rest items))) => (nil (for-each f
(rest items))) => (.invoke nil (for-each f (rest items))) => calling a
method on nil is a NPE
lists are function applications
On Tue, Nov 3, 2009 at 9:33 AM, Dean Wampler wrote:
> I'm working the exercise
> I thought "when" was mainly used for side-effects? "if" seems more
> appropriate if you just want the return value.
It's perfectly appropriate and idiomatic when you want the alternative
return value to be nil, and you don't want to confuse matters by
having a one-element `if`, or an `if` t
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