Not an expert, but I’ll throw out an alternative approach that might work for
you. I think it’s simpler to use a transducer that calls functions rather than
trying to transform an existing transducer to do the cutoff.
(defn take-while-accumulating [accf init pred2]
(fn [rf]
(let [vstate (volatile! init)]
(fn
([] (rf))
([result] (rf result))
([result input]
(if (pred2 @vstate input)
(do (vswap! vstate accf input)
(rf result input))
(reduced result)))))))
accf is like a reducing function: takes two args, state and input, and returns
new state of the “accumulation”. init is the initial state of the
accumulation. pred2 is a predicate taking two args, the accumulation state and
the new input. The process stops when pred2 returns false.
;; distinct
(into [] (take-while-accumulating conj #{} (complement contains?)) '(1 2 3 4 2
5 6))
;;=> [1 2 3 4]
;; dedupe
(into [] (take-while-accumulating (fn [r x] x) ::void not=) '(1 2 1 3 4 4 5 6))
;;=> [1 2 1 3 4]
;; monotonically increasing
(into [] (take-while-accumulating max 0 <=) '(1 2 3 4 4 1 5 6))
[1 2 3 4 4]
Steve Miner
[email protected]
On May 9, 2015, at 6:28 PM, Andy- <[email protected]> wrote:
> (defn take-while-xf
>
> "Takes a transducer and returns a transducer that will immediately finish (ie
> call (reduced)) when the transducer did not call the reducing function and
> just returned the result. Only really useful with stateful transducers.
> Otherwise you'd use take-while."
>
> [xf]
>
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