[erlang-questions] list:join() for erlang?

Peter K Chan <>
Thu Sep 13 16:26:58 CEST 2007


That would be a great help! It would be great if this functionality can
make it into the official package.

Peter

-----Original Message-----
From: Kenneth Lundin [mailto:] 
Sent: Thursday, September 13, 2007 1:39 AM
To: Peter K Chan
Cc: ok; erlang-questions Questions
Subject: Re: [erlang-questions] list:join() for erlang?

We are considering adding a string:join(ListOfStrings,
SeparatorString) -> String
in the next release. Note that String is a list of integers.

/Kenneth (Erlang/OTP team at Ericsson)

On 9/13/07, Peter K Chan <> wrote:
> Yes, the list of lists was what I meant. :)
>
> I wanted Python/Ruby style join, where the function can take any
> arbitrary separator.
>
> I already have the code, so I am looking for either information on
where
> to find such functionality in OTP (if it is hidden in some obscure
> module), or to suggest that such a function be added to lists or
strings
> by OTP.
>
> Peter
>
> -----Original Message-----
> From: 
> [mailto:] On Behalf Of ok
> Sent: Wednesday, September 12, 2007 6:01 PM
> To: erlang-questions Questions
> Subject: Re: [erlang-questions] list:join() for erlang?
>
> On 13 Sep 2007, at 4:26 am, Peter K Chan wrote:
>
> > Sorry that I made an omission.
> >
> > I was referring to the variant of join which takes a separator. For
> > example: lists:join("abc", "/"), which evaluates to "a/b/c".
>
> Should that have been join(["a","b","c"], "/")?
>
> There are filename:join/2 and filename:join/1 functions which come
> close to what you want, but they are specialised to file names and
> do stuff you may not want.  On the other hand, if, as the slash
> suggests, you are pasting file names together, then filename:join/1
> is EXACTLY what you want.
>
> Otherwise, if what you are after is the Python join(words, sep)
> function, you want the code below.  As you note, it isn't that hard
> to write, but then, neither are most of the functions in the lists
> and string modules.  This doesn't depend on the element type, so it
> could go in the lists module, but considering its likely uses, it
> probably belongs in the string module.
>
> %   join([X1,...,Xn], Sep) -> X1 ++ Sep ++ ... ++ Sep ++ Xn;
> %   join([],          _)   -> [].
> %   The intended type is join([[x]], [x]) -> [x].
>
> join([X|Xs], [])  -> join0(X, Xs);
> join([X|Xs], [C]) -> join1(X, C, Xs);
> join([X|Xs], Sep) -> join2(X, Sep, Xs);
> join([],     _)   -> [].
>
> join0(X, [Y|Ys]) -> X ++ join0(Y, Ys);
> join0(X, [])     -> X.
>
> join1(X, C, [Y|Ys]) -> X ++ [C|join1(Y, C, Ys)];
> join1(X, _, [])     -> X.
>
> join2(X, Sep, [Y|Ys]) -> X ++ (Sep ++ join2(Y, Sep, Ys));
> join2(X, _,   [])     -> X.
>
>
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