Question

I have the following function that takes a number like 5 and creates a list of all the numbers from 1 to that number so create(5). returns [1,2,3,4,5].

I have over used guards I think and was wondering if there is a better way to write the following:

create(N) ->
    create(1, N).

create(N,M) when N =:= M ->
    [N];
create(N,M) when N < M ->
    [N] ++ create(N + 1, M).

Answer 1

create(N,N) -> [N];
create(N,M) -> [N|create(N + 1, M)]. % Don't use ++ to prefix a single element.

This isn’t quite the same (you could supply -5), but it behaves the same if you supply meaningful inputs. I wouldn’t bother with the extra check anyway, since the process will crash very quickly either way.

BTW, you have a recursion depth problem with the code as-is. This will fix it:

create(N) ->
    create(1, N, []).

create(N, N, Acc) -> [N|Acc];
create(N, M, Acc) -> create(N, M - 1, [M|Acc]).