Re: reverse a list. is this a good solution

Yes, I noticed and I try to understand
the difference :

I think you mean this function :

let rec aux_rev l accum =

DoI understand that this part in aux_rev[] takes care of a empty
acc ?

I find this solution a little bit confusing expecially the in part
.

Roelof

Matthieu Dubuget [email protected] [ocaml_beginners]
schreef op 20-10-2014 19:42:

Have a second look at Chingfan Tsao post.

He gives you the solution.

Yes: l2 was renamed to accum. This is because it is an
accumulator that is growing during the calls, and returns
the result at the end.

You'll notice that inside rev_list_tail_rec, a hidden
function is defined, and called. During this call, accum
is initialized.

Best regards

Le 20/10/2014 17:56, Roelof
Wobben [email protected]
[ocaml_beginners] a écrit :

Oke,

If I look it it seems to me that acc does the same as
l2 on my programm.

But does acc not have to be intialized on some way ?

Sébastien

then the outcome will be :

string list = ["c"; "b"; "a"; "1"; "2"; "3"]

so it reverse the second string and not the first one.

Roelof

Chingfan Tsao [email protected]
[ocaml_beginners] schreef op 20-10-2014 15:55:

Hi,

It is indeed a good way to solve it since
it's tail recursion, however, there's one more
thing to do to make it easier, wrap it with a
more convenient function:

let rev_list_tail_rec l =

let rec aux_rev l accum =

match l with

| [] -> accum

| h :: tl ->

aux_rev tl (h::accum)

in

aux_rev l []

this way, you can just use rev_list_tail_rec
l instead of having to give one more [] as the
initial value of the accumulator.

2014-10-20 18:56
GMT+08:00 Roelof Wobben [email protected]
[ocaml_beginners] <[email protected] >:

Hello,

I try the 99 ocaml problems and have
solved the reverse a list problem.

My solution looks like this :

let rec test l1 l2 =

match l1 with

| [] -> l2

| h :: t -> test t (h::l2)

;;

Is this a good way to solve it or
are there things that can be better
?

Roelof

--

曹竞帆

哈尔滨工业大学计算机科学与技术专业本科在读

哈尔滨工业大学IBMTC成员

--
Matthieu Dubuget
Guide d’autodéfense numérique : http://guide.boum.org

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