Unexpected results with lists:reverse/1

Questions / Help
#1

Hi all,
I’ve just started programming Erlang, to evaluate if is useful for my company.
But…I’ve immediately got a (stupid?) problem. Here’s the code:

-module(hello).

-export([range/2]).

private_range(1, F) ->
    [F(1)];
private_range(N, F) ->
    [F(N) | range(N - 1, F)].

range(N, F) ->
    lists:reverse(private_range(N, F)).

why the result is

36> hello:range(8, fun(N) -> N end).    
[7,5,3,1,2,4,6,8]

instead of

[1,2,3,4,5,6,7,8]

thanks,
regards,
G.

3 Likes
#2

Maybe you mean

private_range(1, F) ->
    [F(1)];
private_range(N, F) ->
    [F(N) | private_range(N - 1, F)].

?

4 Likes
#3

ops yeah sorry

2 Likes
#4

That outcome is kinda cool, though :smile:

6 Likes
#5 
[1 | [2 | [3]]] = [1, 2, 3]

you are already putting the stuff ordered but without using tail-recursive.

private_range(N, F) ->
    private_range(N, F, []).

private_range(0, _F, Acc) ->
   lists:reverse(Acc);
private_range(N, F, Acc) ->
    private_range(N - 1, F, [F(N) | Acc]).
1 Like