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-module(calc).
-export([factor/1]).
factor(Input) ->
{Tail, Number2} = parseNumber(Input, []),
{_, Result} = factorExtended(Tail, Number2),
Result.
factor(Input, Number1) when is_integer(Number1) or is_float(Number1) ->
{Tail, Number2} = parseNumber(Input, []),
Result = math:pow(Number1, Number2),
factorExtended(Tail, Result);
factor([], Number) ->
{[], Number}.
factorExtended([$^|Tail], Result) ->
factor(Tail, Result);
factorExtended(Tail, Result) ->
{Tail, Result}.
parseNumber([$ |Input], []) ->
%% skip spaces at start
parseNumber(Input, []);
parseNumber([$-|Input], []) ->
parseNumber(Input, "-");
parseNumber([Current|Input], Number) when ($0 =< Current) and ($9 >= Current) ->
parseNumber(Input, Number ++ [Current]);
parseNumber(Input, Number) ->
{Input, list_to_integer(Number)}.
%% eval(Formular) ->
%% term(Formular,[]).
%% term([" "|Input], Parsed) ->
%% term(Input, Parsed);
%% term([Current|Formular], Parsed) ->
%% {ParsedFirst, Number1} = parseNumber([Current|Formular], []).
%% parseOperator([$ |Input]) ->
%% parseOperator(Input);
%% parseOperator([Operator|Input]) ->
%% {ok, list_to_atom(Operator)};
%% parseOperator([]) ->
%% {error, unexpected_end_of_input}.
%% sum(Number1, Number2, '+') ->
%% {ok, Number1 + Number2};
%% sum(Number1, Number2, '-') ->
%% {ok, Number1 - Number2};
%% sum(_, _, _) ->
%% {error, invalid_operator}.
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