[erlang-questions] Idiomatic Erlang, style/performance question
Wed Jun 18 23:19:19 CEST 2008
Circular Function wrote:
> Is there a styleguide somewhere on Erlang? Im currently going through
> the Erlang reference manual and you can see some examples, are those
> generally referred to as idiomatic Erlang?
> Some examples of implementations of the power-function below.
> The last function someone on the mailing list provided as a correction
> to the second one.
> The first one uses pattern matching and guard sequences right? Is this
> a good way? I dont quite understand the advantage of the last function.
> However, the shell complains about
> 88> c(mymath).
> ./mymath.erl:24: Warning: variable 'N' is unused
> Which is the powerx(N, 0) -> 1; line.
> However i saw some code that used _ and i tried:
> powerx(_, 0) -> 1;
> so _ is the correct way to write this function?
I claim no great expertise, but I believe that
power(_N, 0) -> 1;
is the preferred style today: the compiler gives no warning but, should
the need arise, you can refer to the first parameter as _N. (The _Name
style also allows for name which have documentary value)
> Hmm while writing I got a thought. Is the last function
> tail-recursive? I have only heard that term but never used it.
> Is tail-recursion faster or uses less memory, what is the
> power(N, P) when is_integer(N), N >= 0 ->
> ipower(N, P, 1);
> power(N, P) when is_integer(N), N < 0 ->
> 1/ipower(-N, P, 1).
> ipower(0, _, R) -> R;
> ipower(N, P, R) -> ipower(N-1, P, R*P).
Yup, this looks tail recursive, because the recursive call to ipower is
the last thing in the function.
TR functions can run in constant stack space; to write a server you must
use tail recursion.
|Deryk Barker, Computer Science Dept. | Music does not have to be understood|
|Camosun College, Victoria, BC, Canada| It has to be listened to. |
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