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tip for tail recursive map
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Date: -- (:)
From: Julien Verlaguet <julien.verlaguet@g...>
Subject: Re: [Caml-list] tip for tail recursive map
Thanks for the tip !

I used this trick on every function of the List module and didn't try to go
a step further in specific cases.
Main problem being List.fold_right ... I couldn't figure out a way to encode
a more efficient continuation encoding
than the good old CPS, any ideas ?

Thanks

2009/11/2 Damien Doligez <damien.doligez@inria.fr>

>
> On 2009-10-23, at 21:55, pikatchou pokemon wrote:
>
>  I know this topic has been discussed several times, but I don't think I
>> have seen the solution I use for functions of the List module which are not
>> tail recursive.
>> I thought sharing the tip could be nice.
>> I will take an example, List.map.
>> When rewritten in CPS map becomes:
>>
>> let rec map k f = function
>>  | []    -> k []
>>  | x :: rl -> map (fun res -> k ((f x) :: res)) f rl
>>
>
> You can do better with an ad-hoc encoding of the continuation
> instead of using closures:
>
>
> let rec map k f = function
>  | [] -> List.rev k
>  | x :: rl -> map (f x :: k) f rl
> ;;
>
> The memory footprint is smaller, and you spend much less time
> invoking closures.
>
> Note that I haven't bothered benchmarking these two functions.
>
> -- Damien
>
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