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authorRichard Carlsson <[email protected]>2014-12-23 14:23:35 +0100
committerRichard Carlsson <[email protected]>2015-05-22 12:43:53 +0200
commite533ea29e80a641f247022f321a3bf1a1456c56e (patch)
tree2681e4a828e5393d1cc5c539efd5285b92419fa2 /lib/syntax_tools/examples/merl/basic.erl
parent9a81b28598fadc44bf506354c9227e41aac786f6 (diff)
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Include Merl in Syntax Tools
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diff --git a/lib/syntax_tools/examples/merl/basic.erl b/lib/syntax_tools/examples/merl/basic.erl
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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.