Re: [Caml-list] Why List.map does not be implemented tail-recursively?

[Yaron Minsky <yminsky@janestreet.com>]

Agreed.  To be clear, there's a "hack" in Core_kernel's List module
that does more or less what is described, but the gluing together
isn't hacky, i.e., uses no Obj.magic and no mutation.  It's both fast
for short lists and doesn't blow the stack for long lists.

y

On Mon, Sep 29, 2014 at 10:02 AM, Pierre Chambart
<pierre.chambart@laposte.net> wrote:
> On 29/09/2014 14:08, Goswin von Brederlow wrote:
>> And I'll will do the same, reply anyway.
>>
>> You can't write List.map tail recursive unless:
>>
>> 1) You use List.rev (List.rev_map fn list).
>>
>> or
>>
>> 2) Use hacks to create a mutable list so you can grow it head to tail
>> instead of tail to head.
>>
>> The fastest code seems to be when you do List.map recursively up to
>> some limit (say 1000 items) and return the remainder. Repeat and glue
>> the lists together into one large list using hacks.
>>
>> MfG
>>       Mrvn
>>
> Please, don't do that hack ! The compiler assumes immutable data are not
> mutated and optimise knowing that.
> --
> Pierre
>
>
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