[Caml-list] reverse a list

[Caml-list] reverse a list

[Roelof Wobben]

Helllo,

Im a beginner which tries to do the 99 ocaml problems.

Now I try to reverse a list.
Does I need to use two list . one for the old one and one for the 
reversed list.

Roelof

Re: [Caml-list] reverse a list

[Gabriel Scherer]

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Yes.

As an intermediate step, you should consider implementing the function
  reverse_append : 'a list -> 'a list -> 'a list
such that (reverse_append li1 li2) adds li1 *reversed* on top of li2. For
example, reverse_append [1;2] [3;4] is [2;1;3;4].

Is there a particular reason why you're not using the ocaml_beginners list
anymore?  It's a good list for this kind of questions and, if you perceived
a problem with it, it would be interesting to have some feedback about it.

On Sun, Oct 19, 2014 at 2:07 PM, Roelof Wobben <r.wobben@home.nl> wrote:

> Helllo,
>
> Im a beginner which tries to do the 99 ocaml problems.
>
> Now I try to reverse a list.
> Does I need to use two list . one for the old one and one for the reversed
> list.
>
> Roelof
>
>
> --
> Caml-list mailing list.  Subscription management and archives:
> https://sympa.inria.fr/sympa/arc/caml-list
> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
> Bug reports: http://caml.inria.fr/bin/caml-bugs
>

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Re: [Caml-list] reverse a list

[Malcolm Matalka]

Lists are immutable so you'll be constructing a list as you consume
another list.

Roelof Wobben <r.wobben@home.nl> writes:

> Helllo,
>
> Im a beginner which tries to do the 99 ocaml problems.
>
> Now I try to reverse a list.
> Does I need to use two list . one for the old one and one for the reversed list.
>
> Roelof

Re: [Caml-list] reverse a list

[SF Markus Elfring]

> Now I try to reverse a list.

Would you like to compare the run time properties for different approaches?
1. Use of immutable data structures in the functional programming style

2. Manage a list as a mutable member of a class in an "imperative" and
object-oriented programming style

Regards,
Markus

Re: [Caml-list] reverse a list

[Philippe Wang]

On Sun, Oct 19, 2014 at 2:34 PM, Malcolm Matalka <mmatalka@gmail.com> wrote:
> Lists are immutable so you'll be constructing a list as you consume
> another list.

Please don't formulate it this way, as it sounds to me as if the list
being "consumed" is disappearing (because that's what generally
happens when something is being "consumed").  :-/
To the beginners reading this: well, in OCaml, any given list will
never disappear before it actually becomes useless, and they may be
"consumed" over and over again without any "harm" happening to them.

Re: [Caml-list] reverse a list

[Roelof Wobben]

Philippe Wang schreef op 19-10-2014 15:59:
> On Sun, Oct 19, 2014 at 2:34 PM, Malcolm Matalka <mmatalka@gmail.com> wrote:
>> Lists are immutable so you'll be constructing a list as you consume
>> another list.
> Please don't formulate it this way, as it sounds to me as if the list
> being "consumed" is disappearing (because that's what generally
> happens when something is being "consumed").  :-/
> To the beginners reading this: well, in OCaml, any given list will
> never disappear before it actually becomes useless, and they may be
> "consumed" over and over again without any "harm" happening to them.
>

Thanks all

Now trying to find out how I can add things to the second list. I think 
this can work 2::l2

Roelof

Re: [Caml-list] reverse a list

[Roelof Wobben]

Roelof Wobben schreef op 19-10-2014 17:13:
> Philippe Wang schreef op 19-10-2014 15:59:
>> On Sun, Oct 19, 2014 at 2:34 PM, Malcolm Matalka <mmatalka@gmail.com> 
>> wrote:
>>> Lists are immutable so you'll be constructing a list as you consume
>>> another list.
>> Please don't formulate it this way, as it sounds to me as if the list
>> being "consumed" is disappearing (because that's what generally
>> happens when something is being "consumed").  :-/
>> To the beginners reading this: well, in OCaml, any given list will
>> never disappear before it actually becomes useless, and they may be
>> "consumed" over and over again without any "harm" happening to them.
>>
>
> Thanks all
>
> Now trying to find out how I can add things to the second list. I 
> think this can work 2::l2
>
> Roelof
>

I have found a way :

let rec test l1 l2 =
     match l1 with
     | [] -> l2
     | h :: t -> test t (h::l2)
  ;;

Roelof