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

[Anthony Tavener <anthony.tavener@gmail.com>]

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(Oh, Gabriel beat me to the punch, but I'll add my reply anyway.)

The standard library is a fairly minimal library of basic features. Not a
high-level full-featured library which helps you make good choices. :)

However, the documentation (in .mli files) is fairly clear about what is
tail-recursive or not. And there is rev_map:

val rev_map : ('a -> 'b) -> 'a list -> 'b list
(** [List.rev_map f l] gives the same result as
   {!List.rev}[ (]{!List.map}[ f l)], but is tail-recursive and
   more efficient. *)


On Sun, Sep 28, 2014 at 1:31 PM, Shuai Wang <wangshuai901@gmail.com> wrote:

> 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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