[erlang-questions] list:join() for erlang?
Thu Sep 13 12:34:37 CEST 2007
> 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.
Out of curiosity -- still feeling my way around erlang and functional
programming -- aren't the "helper" functions here stack-recursive (i.e. *not*
In other words "X ++ join(Y, Ys)" would evaluate the recursive calls to join()
before being able to concatenate the result onto X... meaning keeping stuff on
the stack for each call.
Am I right or misinterpreting the call structure?
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