Erlang : Breaking out of lists:foreach "loop"

Question

I have a list of elements in Erlang, and I'm using lists:foreach to traverse through the elements in the list. Is there a way to break out of this "foreach loop" in the middle of the traversal. For eg: suppose I want to stop traversing the list further if I encounter a '1' in the list [2, 4, 5, 1, 2, 5]. How do I do this?

Answer 1

traverse(Liste) ->
 traverse(Liste, []).

traverse([], Acc) ->
 Acc;    

traverse([1|_], Acc) ->
 Acc;

traverse([H|T], Acc) ->
 % do something useful here maybe?
 traverse(T, Acc).

Of course this is very rough example.

Answer 2

Another way to do it is to use throw and catch:

catch lists:foreach(
        fun(1) ->
                throw(found_one);
           (X) ->
                io:format("~p~n", [X])
        end,
        [2, 4, 5, 1, 2, 5]).

When run in the shell, this outputs:

2
4
5
found_one

EDIT: By popular demand, a more precise version that catches only what you want to catch:

try lists:foreach(
        fun(1) ->
                throw(found_one);
           (X) ->
                io:format("~p~n", [X])
        end,
        [2, 4, 5, 1, 2, 5])
catch
    throw:found_one ->
        found_one
end.

Answer 3

There are many nice functions in lists module:

lists:foreach(fun(E) -> do_something(E) end,
    lists:takewhile(fun(E) -> E =/= 1 end, List)).

or more effective but less nice

lists:takewhile(fun(1) -> false;
                   (E) -> do_something(E), true
                end, List)