From 8c8596c17a3c63347574f63c3f93de2b64669720 Mon Sep 17 00:00:00 2001
From: Alexander Sulfrian <alexander@sulfrian.net>
Date: Mon, 11 Oct 2010 20:16:41 +0200
Subject: added factor to parse things like x^y^z...

added factor,
added parseNumber to parse an integer from the input string
---
 calc.erl | 81 +++++++++++++++++++++++++++++++++++++++++-----------------------
 1 file changed, 52 insertions(+), 29 deletions(-)

diff --git a/calc.erl b/calc.erl
index 4bf5967..a24b915 100644
--- a/calc.erl
+++ b/calc.erl
@@ -1,30 +1,53 @@
 -module(calc).
--export([eval/1]).
-
-eval(Formular) ->
-    eval(Formular,[]).
-
-eval([C | Formular], T) when integer(C) ->
-    eval(Formular, parseDigit(T, C));
-
-eval([C | Formular], T) when C == "." ->
-    eval(Formular, parseDigit(T, C));
-
-eval([C | Formular], T) when C == "+" ->
-    eval(Formular, [{plus, C}] ++ T);
-eval([C |Formular], T) when C == "-" ->
-    eval(Formular, [{minus, C}] ++ T);
-eval([C |Formular], T) when C == "*" ->
-    eval(Formular, [{mal, C}] ++ T);
-eval([C |Formular], T) when C == "/" ->
-    eval(Formular, [{durch, C}] ++ T);
-
-eval([], P) ->
-    P.
-
-parseDigit([{digit, Last} | Tail], Current) when list(Last) ->
-    [{digit, Last ++ Current} | Tail];
-parseDigit([{digit, Last} | Tail], Current) ->
-    [{digit, [Last] ++ Current} | Tail];
-parseDigit(Tail, Current) ->
-    [{digit, Current} | Tail].
+-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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