Ranges in Erlang

Question

From the other languages I program in, I'm used to having ranges. In Python, if I want all numbers one up to 100, I write range(1, 101). Similarly, in Haskell I'd write [1..100] and in Scala I'd write 1 to 100.

I can't find something similar in Erlang, either in the syntax or the library. I know that this would be fairly simple to implement myself, but I wanted to make sure it doesn't exist elsewhere first (particularly since a standard library or language implementation would be loads more efficient).

Is there a way to do ranges either in the Erlang language or standard library? Or is there some idiom that I'm missing? I just want to know if I should implement it myself.

I'm also open to the possibility that I shouldn't want to use a range in Erlang (I wouldn't want to be coding Python or Haskell in Erlang). Also, if I do need to implement this myself, if you have any good suggestions for improving performance, I'd love to hear them :)

Answer 1

From http://www.erlang.org/doc/man/lists.html it looks like lists:seq(1, 100) does what you want. You can also do things like lists:seq(1, 100, 2) to get all of the odd numbers in that range instead.

Answer 2

You can use list:seq(From, TO) that's say @bitilly, and also you can use list comprehensions to add more functionality, for example:

1> [X || X <- lists:seq(1,100), X rem 2 == 0].
[2,4,6,8,10,12,14,16,18,20,22,24,26,28,30,32,34,36,38,40,42,
 44,46,48,50,52,54,56,58|...]

Answer 3

There is a difference between range in Ruby and list:seq in Erlang. Ruby's range doesn't create list and rely on next method, so (1..HugeInteger).each { ... } will not eat up memory. Erlang lists:seq will create list (or I believe it will). So when range is used for side effects, it does make a difference.

P.S. Not just for side effects:

(1..HugeInteger).inject(0) { |s, v| s + v % 1000000 == 0 ? 1 : 0 }

will work the same way as each, not creating a list. Erlang way for this is to create a recursive function. In fact, it is a concealed loop anyway.