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%% ---------------------------------------------------------------------
%% Licensed under the Apache License, Version 2.0 (the "License"); you may
%% not use this file except in compliance with the License. You may obtain
%% a copy of the License at <http://www.apache.org/licenses/LICENSE-2.0>
%%
%% Unless required by applicable law or agreed to in writing, software
%% distributed under the License is distributed on an "AS IS" BASIS,
%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%% See the License for the specific language governing permissions and
%% limitations under the License.
%%
%% @author Richard Carlsson <[email protected]>
%% @copyright 2012 Richard Carlsson
%% @doc Trivial Basic interpreter in Erlang
-module(basic).
-export([run/2]).
-include_lib("eunit/include/eunit.hrl").
-define(INTERPRETED, true).
-include("basic_test.erl").
run(N, Prog) ->
ets:new(var, [private, named_table]),
ets:new(line, [private, named_table, ordered_set]),
lists:foreach(fun (T) -> ets:insert(line, T) end, Prog),
goto(N).
stop(N) ->
ets:delete(var),
ets:delete(line),
N.
goto('$end_of_table') -> stop(0);
goto(L) ->
L1 = ets:next(line, L),
%% user-supplied line numbers might not exist
case ets:lookup(line, L) of
[{_, X}] ->
stmt(X, L1);
_ ->
goto(L1)
end.
stmt({print, S, As}, L) -> io:format(S, [expr(A) || A <- As]), goto(L);
stmt({set, V, X}, L) -> ets:insert(var, {V, expr(X)}), goto(L);
stmt({goto, X}, _L) -> goto(expr(X));
stmt({stop, X}, _L) -> stop(expr(X));
stmt({iff, X, A, B}, _L) ->
case expr(X) of
0 -> goto(B);
_ -> goto(A)
end.
expr(X) when is_number(X) ; is_list(X) ->
X;
expr(X) when is_atom(X) ->
case ets:lookup(var, X) of
[] -> 0;
[{_,V}] -> V
end;
expr({plus, X, Y}) ->
expr(X) + expr(Y);
expr({equal, X, Y}) ->
bool(expr(X) == expr(Y));
expr({gt, X, Y}) ->
bool(expr(X) > expr(Y));
expr({knot, X}) ->
case expr(X) of
0 -> 1;
_ -> 0
end.
bool(true) -> 1;
bool(false) -> 0.
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