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

[Shuai Wang <wangshuai901@gmail.com>]

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Wow, List.rev_map f (List.rev li) looks very elegant, thank you all for the
helpful materials! I should definitely try Core lib soon.

I have been working on a binary program analysis project for over half a
year in OCaml, and it is really enjoyable to write OCaml code!
hope I can open source the analysis tool eventually and contribute to the
community :)

Best,
Shuai



On Sun, Sep 28, 2014 at 4:26 PM, Yaron Minsky <yminsky@janestreet.com>
wrote:

> Indeed, the implementation from that post did make it into
> Core_kernel.  Here's the link:
>
>
> https://github.com/janestreet/core_kernel/blob/release-112.01.00/lib/core_list.ml#L380
>
> y
>
> On Sun, Sep 28, 2014 at 3:45 PM, Malcolm Matalka <mmatalka@gmail.com>
> wrote:
> > https://blogs.janestreet.com/optimizing-list-map/
> >
> > And from the horse's mouth:
> >
> > https://groups.google.com/forum/#!msg/fa.caml/YaLYqkpn928/1jdo8a0K6AEJ
> >
> > Shuai Wang <wangshuai901@gmail.com> writes:
> >
> >> Hello list,
> >>
> >>
> >> I am working on some stack_overflow exception in our recent project
> written
> >> in OCaml
> >> and eventually it turns out that this exception is thrown by List.map
> >> function.
> >>
> >> By seeing the source code of OCaml's List module
> >> <
> https://code.ohloh.net/file?fid=P5Us_txNCMHIhpdfML6OZ8QN4Zs&cid=Jigg8RAfQdg&s=ocaml%20list.ml&pp=0&fp=305967&fe=ml&ff=1&filterChecked=true&mp=1&ml=1&me=1&md=1#L3
> >,
> >> it seems that map function
> >> does not be implemented tail-recursively:
> >>
> >> let rec map f = function
> >>     [] -> []
> >>   | a::l -> let r = f a in r :: map f l
> >>
> >>
> >>
> >> So my question is:
> >>
> >> *Why would OCaml's implementation List.map like this?  *
> >>
> >> In my humble option, it definitely should be written in a tail-recursive
> >> way,
> >> and it not, stack_overflow would be unavoidable.
> >> For example in order to handle the exception,
> >> I abandon the code using List.map and rewrite it into a tail-recursive
> help
> >> function.
> >>
> >> Best,
> >> Shuai
> >
> > --
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