//syntax: if <test> <consequent> <alternate>
//syntax: if <test> <consequent>
public override Node eval(Node exp, Environment env)
{
var length = Node.length(exp);
if (length < 3 || length > 4)
{
Console.Error.WriteLine("Error: Invalid length for if expression");
return(Nil.getInstance());
}
var test = exp.getCdr().getCar();
var consequent = exp.getCdr().getCdr().getCar();
var alternate = new Node();
if (length == 4) //has alternates
{
alternate = exp.getCdr().getCdr().getCdr().getCar();
}
else //If <test> yields a false value and no <alternate> is specified, then the result of the expression is unspecified.
{
alternate = Unspecific.getInstance();
}
if (test.eval(env) != BoolLit.getInstance(false))
{
return(consequent.eval(env));
}
return(alternate.eval(env));
}
private Node apply0()
{
string name = symbol.getName();
if (name.Equals("read"))
{
var parser = new Parser(new Scanner(Console.In), new TreeBuilder());
var exp = (Node)parser.parseExp();
if (exp != null)
{
return(exp);
}
return(new Ident("end-of-file"));
}
if (name.Equals("newline"))
{
Console.WriteLine();
return(Unspecific.getInstance());
}
if (name.Equals("interaction-environment"))
{
return(Scheme4101.env);
}
Console.Error.WriteLine("Error: wrong number of arguments");
return(Nil.getInstance());
}
private Node apply2(Node arg1, Node arg2)
{
string name = symbol.getName();
if (name.Equals("eq?"))
{
if (arg1.isSymbol() && arg2.isSymbol())
{
return(BoolLit.getInstance(arg1.getName().Equals(arg2.getName())));
}
return(BoolLit.getInstance(arg1 == arg2));
}
if (name.Equals("cons"))
{
return(new Cons(arg1, arg2));
}
if (name.Equals("set-car!"))
{
arg1.setCar(arg2);
return(Unspecific.getInstance());
}
if (name.Equals("set-cdr!"))
{
arg1.setCdr(arg2);
return(Unspecific.getInstance());
}
if (name.Equals("eval"))
{
if (arg2.isEnvironment())
{
Environment envArg1 = (Environment)arg1;
return(arg1.eval(envArg1));
}
Console.Error.WriteLine("Error: argument is not an environment");
return(Nil.getInstance());
}
if (name.Equals("apply"))
{
return(arg1.apply(arg2));
}
if (name[0].Equals('b') && name.Length == 2)
{
if (arg1.isNumber() && arg2.isNumber())
{
return(evalArithmetic(arg1.getIntVal(), arg2.getIntVal()));
}
Console.Error.WriteLine("Error: invalid arguments");
return(Nil.getInstance());
}
Console.Error.WriteLine("Error: wrong number of arguments");
return(Nil.getInstance());
}
private Node evalClauses(Node exp, Environment env)
{
if (exp.isNull())
{
return(Unspecific.getInstance());
}
var clause = exp.getCar();
if (Node.length(clause) <= 0)
{
Console.Error.WriteLine("Error: invalid cond expression");
return(Nil.getInstance());
}
var testExp = clause.getCar();
var expression = clause.getCdr();
if (testExp.isSymbol() && testExp.getName().Equals("else"))
{
if (!expression.isNull() && exp.getCdr().isNull())
{
return(evalExp(expression, env));
}
Console.Error.WriteLine("Error: invalid expression");
return((Node)Nil.getInstance());
}
var testValid = testExp.eval(env);
if (testValid == BoolLit.getInstance(false))
{
var nextExps = exp.getCdr();
return(evalClauses(nextExps, env));
}
if (expression.isNull())
{
return(BoolLit.getInstance(true));
}
var exp1 = expression.getCar();
if (!exp1.isSymbol() || !exp1.getName().Equals("=>"))
{
return(evalExp(expression, env));
}
if (Node.length(expression) != 2)
{
Console.Error.WriteLine("Error: invalid cond expression");
return(Nil.getInstance());
}
var cdr = expression.getCdr().getCar();
return(cdr.eval(env).apply(BoolLit.getInstance(true)));
}
public override Node eval(Node exp, Environment env)
{
if (Node.length(exp) != 3)
{
Console.Error.WriteLine("Error: invalid set expression");
return((Node)Nil.getInstance());
}
Node var = exp.getCdr().getCar();
Node varExp = exp.getCdr().getCdr().getCar();
env.assign(var, varExp.eval(env));
return(Unspecific.getInstance());
}
private Node apply1(Node arg1)
{
string name = symbol.getName();
if (name.Equals("car"))
{
return(arg1.getCar());
}
if (name.Equals("cdr"))
{
return(arg1.getCdr());
}
if (name.Equals("number?"))
{
return(BoolLit.getInstance(arg1.isNumber()));
}
if (name.Equals("symbol?"))
{
return(BoolLit.getInstance(arg1.isSymbol()));
}
if (name.Equals("null?"))
{
return(BoolLit.getInstance(arg1.isNull()));
}
if (name.Equals("pair?"))
{
return(BoolLit.getInstance(arg1.isPair()));
}
if (name.Equals("procedure?"))
{
return(BoolLit.getInstance(arg1.isProcedure()));
}
if (name.Equals("write"))
{
arg1.print(-1);
return(Unspecific.getInstance());
}
if (name.Equals("display"))
{
Console.Write(arg1);
return(Unspecific.getInstance());
}
Console.Error.WriteLine("Error: wrong number of arguments");
return(Nil.getInstance());
}