An Erlang implementation of the String calculator kata. Regular Expressions are for sissies. http://osherove.com/tdd-kata-1/

stringcalc.erl

-module(stringcalc).
-export([add/1, test/0]).

%% Test methods. 
%% Returns ok if all is well. 
test() ->
	3 = add("1,2"),
	0 = add(""),
	1 = add("1"),
	6 = add("1\n2,3"),
	3 = add("//;\n1;2"),
	6 = add("//[*][%]\n1%2*3"),
	6 = add("//[****]\n1****2****3"),
	2 = add("2,1001"),
	ok.

%%% Implementation of the add method
add([]) -> 0;
add(String) ->
	{Delim, NewString} = extract_delims(String),
	Numbers = lists:map(fun(X) -> 
		{Int, _} = string:to_integer(X), Int end,
		string:tokens(NewString, Delim)),
	sum(Numbers).

extract_delims([$/, $/ | Tail]) ->
	{FirstLine, Numberstring} = lists:splitwith(fun(S) -> S =/= $\n end, Tail),
	Delims = delimiters(FirstLine),
	{Delims, string:substr(Numberstring, 2)};
extract_delims(String) ->
	{",\n", String}.

delimiters(FirstLine) -> 
	lists:flatten(string:tokens(FirstLine, "[]")). 

sum(Numbers) ->
	sum(Numbers, 0).

sum([], Acc) -> Acc;
sum([H|_], _) when H < 0 -> throw("Negative number!!");
sum([H|T], Acc) when H > 1000 -> sum(T, Acc);
sum([H|T], Acc) -> sum(T, Acc+H).