%%% BEGIN pibfi_tape_tuple.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 Tuple backend for tape ADT for <code>pibfi</code>.
%%
%% @end

-module(pibfi_tape_tuple).
-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, increment/2, decrement/2]).
-export([read/1, write/2, peek/2, poke/3, head/1]).

%% @spec new([option()]) -> tape()
%%         option() = {atom(), term()}
%%         tape() = tape()
%% @doc Creates and returns a new tuple-backed tape.

new(Options) ->
  0 = pibfi_options:get_option(Options, mintape, 0),
  Max = pibfi_options:get_option(Options, maxtape, 30000),
  {1, erlang:make_tuple(Max, 0)}.

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

left({Position, Tuple}, N)
 when (Position - N) >= 1 ->
  {{Position - N, Tuple}, element(Position - N, Tuple)}.

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

right({Position, Tuple}, N)
 when (Position + N) =< size(Tuple) ->
  {{Position + N, Tuple}, element(Position + N, Tuple)}.

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

read({Position, Tuple}) -> element(Position, Tuple).

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

write({Position, Tuple}, Value) ->
  {{Position, setelement(Position, Tuple, Value)}, Value}.

%% @spec increment(tape(), N::integer()) -> tape()
%% @doc Increments the value at the current position on the tape N times.

increment(Tape, N) ->
  write(Tape, read(Tape) + N).

%% @spec decrement(tape(), N::integer()) -> tape()
%% @doc Decrements the value at the current position on the tape N times.

decrement(Tape, N) ->
  write(Tape, read(Tape) - N).

peek({Position, Tuple}, Addr) ->
  element(Addr + 1, Tuple).

poke({Position, Tuple}, Addr, Value) ->
  {Position, setelement(Addr + 1, Value, Tuple)}.

head({Position, Tuple}) ->
  Position - 1.
  
%%% END of pibfi_tape_tuple.erl %%%