fix exception if no input

1 files changed, 2 insertions, 0 deletions

diff --git a/calc.erl b/calc.erl
index b7981a1..04ac38f 100644
--- a/calc.erl
+++ b/calc.erl
@@ -9,6 +9,8 @@ num([Current|Input], Num) when ($0 =< Current) and ($9 >= Current) ->
     num(Input, Num ++ [Current]);
 num([Head|_], "-") ->
     {error, {unexpected, list_to_atom([Head])}};
+num(Input, []) ->
+    {ok, {Input, []}};
 num(Input, Num) ->
     {ok, {Input, list_to_integer(Num)}}.