(use 'clojure.contrib.seq-utils)
(def by-pairs
(partial partition-all 2 1))
; ignores possibility of nil (exercise for reader)
(defn matched-pair?
[[a b]]
(= a b))
; I think this is very literate
(println (let [x [1 2 3 4 5 5 5 6]]
(->> (by-pairs x)
(remove matched-pair?)
(map first))))
The first thing I can think of is that filter is lazy. You side
effects won't occur when you think they will. Generally if you're
dealing with side-effects over a sequence, it's time to think about
using a macro, such as doseq.
In your specific case, I'd recommend using a custom form of reduce,
something that returned
[your-filtered-seq last-element]
HTH,
Sean
On Feb 18, 9:04 am, Rowdy Rednose <rowdy.redn...@gmx.net> wrote:
The filter documentation reads:
"Returns a lazy sequence of the items in coll for which (pred item)
returns true. pred must be free of side-effects."
So that means I should not write a function like this:
(defn unique [sc]
"Returns a lazy sequence with all consecutive duplicates removed"
(let [last (atom (Object.))]
(filter #(let [ok (not= @last %)] (reset! last %) ok) sc)))
user=> (unique [1 2 3 3 4 5 5 6])
(1 2 3 4 5 6)
But in contrast to functions that can be retried (compare-and-swap
etc.), I don't immediately see why having side effects in filter
would
be bad. Can anybody enlighten me? And how should I do this instead?
Thanks
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