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/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.
*/
/* $Rev$ $Date$ */
#ifndef tuscany_scheme_environment_hpp
#define tuscany_scheme_environment_hpp
/**
* Script evaluator environment implementation.
*/
#include "string.hpp"
#include "list.hpp"
#include "value.hpp"
#include "primitive.hpp"
#include <string>
namespace tuscany {
namespace scheme {
typedef value Frame;
typedef list<value> Env;
const value trueSymbol("true");
const value falseSymbol("false");
const value defineSymbol("define");
const value setSymbol("set!");
const value dotSymbol(".");
const Env theEmptyEnvironment() {
return list<value>();
}
const bool isDefinition(const value& exp) {
return isTaggedList(exp, defineSymbol);
}
const bool isAssignment(const value& exp) {
return isTaggedList(exp, setSymbol);
}
const bool isVariable(const value& exp) {
return isSymbol(exp);
}
const Env enclosingEnvironment(const Env& env) {
return cdr(env);
}
const gc_ptr<Frame> firstFrame(const Env& env) {
return car(env);
}
list<value> frameVariables(const Frame& frame) {
return car((list<value> )frame);
}
list<value> frameValues(const Frame& frame) {
return cdr((list<value> )frame);
}
const bool isDotVariable(const value& var) {
return var == dotSymbol;
}
const Frame makeBinding(const Frame& frameSoFar, const list<value>& variables, const list<value> values) {
if (isNil(variables)) {
if (!isNil(values))
logStream() << "Too many arguments supplied " << values << endl;
return frameSoFar;
}
if (isDotVariable(car(variables)))
return makeBinding(frameSoFar, cdr(variables), mklist<value>(values));
if (isNil(values)) {
if (!isNil(variables))
logStream() << "Too few arguments supplied " << variables << endl;
return frameSoFar;
}
const list<value> vars = cons(car(variables), frameVariables(frameSoFar));
const list<value> vals = cons(car(values), frameValues(frameSoFar));
const Frame newFrame = cons(value(vars), vals);
return makeBinding(newFrame, cdr(variables), cdr(values));
}
const gc_ptr<Frame> makeFrame(const list<value>& variables, const list<value> values) {
gc_ptr<Frame> frame = new (gc_new<Frame>()) Frame();
*frame = value(makeBinding(cons(value(list<value>()), list<value>()), variables, values));
return frame;
}
const value definitionVariable(const value& exp) {
const list<value> exps(exp);
if(isSymbol(car(cdr(exps))))
return car(cdr(exps));
const list<value> lexps(car(cdr(exps)));
return car(lexps);
}
const value definitionValue(const value& exp) {
const list<value> exps(exp);
if(isSymbol(car(cdr(exps))))
return car(cdr(cdr(exps)));
const list<value> lexps(car(cdr(exps)));
return makeLambda(cdr(lexps), cdr(cdr(exps)));
}
const value assignmentVariable(const value& exp) {
return car(cdr((list<value> )exp));
}
const value assignmentValue(const value& exp) {
return car(cdr(cdr((list<value> )exp)));
}
const Frame addBindingToFrame(const value& var, const value& val, const Frame& frame) {
return cons(value(cons(var, frameVariables(frame))), cons(val, frameValues(frame)));
}
const bool defineVariable(const value& var, const value& val, Env& env) {
*firstFrame(env) = addBindingToFrame(var, val, *firstFrame(env));
return true;
}
const Env extendEnvironment(const list<value>& vars, const list<value>& vals, const Env& baseEnv) {
return cons<value>(makeFrame(vars, vals), baseEnv);
}
const Env setupEnvironment() {
Env env = extendEnvironment(primitiveProcedureNames(), primitiveProcedureObjects(), theEmptyEnvironment());
defineVariable(trueSymbol, true, env);
defineVariable(falseSymbol, false, env);
return env;
}
const value lookupEnvLoop(const value& var, const Env& env);
const value lookupEnvScan(const value& var, const list<value>& vars, const list<value>& vals, const Env& env) {
if(isNil(vars))
return lookupEnvLoop(var, enclosingEnvironment(env));
if(var == car(vars))
return car(vals);
return lookupEnvScan(var, cdr(vars), cdr(vals), env);
}
const value lookupEnvLoop(const value& var, const Env& env) {
if(env == theEmptyEnvironment()) {
logStream() << "Unbound variable " << var << endl;
return value();
}
return lookupEnvScan(var, frameVariables(*firstFrame(env)), frameValues(*firstFrame(env)), env);
}
const value lookupVariableValue(const value& var, const Env& env) {
return lookupEnvLoop(var, env);
}
}
}
#endif /* tuscany_scheme_environment_hpp */
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