Add task 6 (#4)

* tasks 0,1,2,4

* fix syntax in tasks 1 and 2

* change filter to tail rec

* add task 3

* fix repo?

* task 5

* task 6

* last small fixes

* switch to div, fix error handling

.gitignore

@@ -2,3 +2,4 @@
 .DS_Store
 *.iml
 *.beam
+godocker.sh

task_2_6.erl

@@ -0,0 +1,50 @@
+-module(task_2_6).
+
+%% API
+-export([test/0]).
+
+test() ->
+  process("task_2_6.txt").
+
+process(Filename) ->
+  Row = readcsv(Filename),
+  process_row(Row).
+
+%% process_tokens
+process_row(List) ->
+  process_row(List, [], List).
+
+process_row([], Stack, _) ->
+  lists:reverse(Stack);
+process_row([H|T], Stack, List) ->
+  process_row(T, [parse_cell(H, List) | Stack], List).
+
+%% parse_cell
+parse_cell(Str, List) ->
+  parse_cell(string:tokens(Str, " "), [], List).
+
+parse_cell([], Stack, _) ->
+  case length(Stack) of
+    1 -> hd(Stack);
+    _ -> error(badarg)
+  end;
+parse_cell([Token|Tail], Stack, List) ->
+  case Token of
+    "$" ++ N -> parse_cell(Tail, [parse_cell(lists:nth(list_to_integer(N), List), List) | Stack], List);
+    "+" -> parse_cell(Tail, reduce(fun(A, B) -> A + B end, Stack), List);
+    "-" -> parse_cell(Tail, reduce(fun(A, B) -> A - B end, Stack), List);
+    "*" -> parse_cell(Tail, reduce(fun(A, B) -> A * B end, Stack), List);
+    "/" -> parse_cell(Tail, reduce(fun(A, B) -> A div B end, Stack), List);
+    _ -> parse_cell(Tail, [list_to_integer(Token)|Stack], List)
+  end.
+
+reduce(F, [A,B|Tail]) ->
+  [F(B, A)|Tail];
+reduce(_, _) ->
+  error(badarg).
+
+readcsv(Filename) ->
+  case file:read_file(Filename) of
+    {ok, FileBin} -> string:tokens(erlang:binary_to_list(FileBin), ",\n");
+    {error, Reason} -> error(Reason)
+  end.

task_2_6.txt

@@ -0,0 +1 @@
+$5 $6 +,3,6,4,2 $2 +,2,7