CODEWITHSUNDEEP
erlang
user1902535
user1902535

Reputation: 155

Creating a sequence in a list

I am very new to Erlang and I have a question about this function that returns a list counting down in ones. e.g. [3,2,1]

Why doesn't it work if you change the N-1 to N-2?

I'm looking to get the output to show [7,5,3,1]

-module(create_list).
-export([create_list/1]).

create_list(0) ->
       [];

create_list(N) ->
    [ N | create_list(N - 1) ].

Upvotes: 1

Views: 1516

Answers (3)

wudeng
wudeng

Reputation: 815

There is already a function to do this:

lists:seq(From, To, Incr) -> Seq
1> lists:seq(7,1,-2).
[7,5,3,1]

Upvotes: 1

Dmitry Belyaev
Dmitry Belyaev

Reputation: 2593

Safer to use positive check:

create_list(N) when N > 0 ->
   [N | create_list(N - 2)];
create_list(_) ->
   [].

Upvotes: 2

ikegami
ikegami

Reputation: 386706

Because no matter how many times you subtract 2 from an odd number, you'll never get zero?

I've never even seen Erlang code before, but I suspect the fix is to add

create_list(1) ->
       [ 1 ];

Upvotes: 4

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