%%% BEGIN pibfi_tape_dict.erl %%%
%%%
%%% pibfi - Platonic Ideal Brainf*ck Interpreter
%%% Copyright (c)2003 Cat's Eye Technologies.  All rights reserved.
%%%
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%%%   from this software without specific prior written permission.
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%% @doc Dict backend for tape ADT for the Platonic Ideal Brainf*ck Interpreter.
%%
%% @end

-module(pibfi_tape_dict).
-vsn('2003.0427').
-copyright('Copyright (c)2003 Cat`s Eye Technologies. All rights reserved.').

-behaviour(pibfi_tape).

-export([new/1]).
-export([left/2, right/2]).
-export([read/1, write/2]).
-export([peek/2, poke/3, head/1]).

%% @spec new([option()]) -> tape()
%%         option() = {atom(), term()}
%%         tape() = tape()
%% @doc Creates and returns a new tape.
%% For a description of the allowed options, see the documentation for
%% the <code><a href="pibfi.html">pibfi</a></code> module.

new(Options) ->
  {0, dict:new()}.

%% @spec left(tape(), N::integer()) -> {tape(), integer()}
%% @doc Moves the read/write head N positions left on the tape.

left({Position, Dict}, N) ->
  {{Position - N, Dict}, read({Position - N, Dict})}.

%% @spec right(tape(), N::integer()) -> {tape(), integer()}
%% @doc Moves the read/write head N positions right on the tape.

right({Position, Dict}, N) ->
  {{Position + N, Dict}, read({Position + N, Dict})}.

%% @spec read(tape()) -> integer()
%% @doc Returns the value at the current position on the tape.

read({Position, Dict}) ->
  case dict:find(Position, Dict) of
    error ->
      0;
    {ok, Value} ->
      Value
  end.

%% @spec write(tape(), integer()) -> {tape(), integer()}
%% @doc Places the given value at the current position on the tape.

write({Position, Dict}, Value) ->
  {{Position, dict:store(Position, Value, Dict)}, Value}.

peek({Position, Dict}, Addr) ->
  read({Addr, Dict}).

poke({Position, Dict}, Addr, Value) ->
  {Position, dict:store(Addr, Value, Dict)}.

head({Position, Dict}) ->
  Position.
  
%%% END of pibfi_tape_dict.erl %%%