Thanks for the reply. I do like this. I think it's actually more elegant.
Definitely going into my toolbox. One thing I dislike is that I still have
to re-implement the logic of the already existing (performant & tested)
transducers.
Also, I could also add a 4th parameter: 'terminate-early?' but that's then
already 4 parameters to remember... I'll have to see what way is best once
I implement more transducers with your or my (hacky) method.
Cheers
On Monday, May 11, 2015 at 1:34:31 PM UTC-4, miner wrote:
>
> 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] <javascript:>
>
>
>
>
> On May 9, 2015, at 6:28 PM, Andy- <[email protected] <javascript:>>
> 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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