public override Node eval(Node exp, Environment env)
{
int length = Util.expLength(exp);
if (length < 3)
{
Console.Error.WriteLine("Error: invalid expression");
return Nil.getInstance();
}
Node second = exp.getCdr().getCar();
Node name, value;
if (length == 3 && second.isSymbol())
{
name = second;
value = exp.getCdr().getCdr().getCar().eval(env);
env.define(name, value);
return null;
}
if (!second.isPair())
{
Console.Error.WriteLine("Error: invalid expression");
return Nil.getInstance();
}
name = second.getCar();
Node lambda = exp.getCdr();
lambda.setCar(second.getCdr());
lambda = new Cons(new Ident("lambda"), lambda);
value = lambda.eval(env);
env.define(name, value);
return null;
}
// TODO: The method apply() should be defined in class Node
// to report an error. It should be overridden only in classes
// BuiltIn and Closure.
public override Node apply(Node args)
{
Environment funcEnvironment = new Environment(env);
Node param = fun.getCdr().getCar();
while (param != Nil.getInstance() && args != Nil.getInstance())
{
funcEnvironment.define(param.getCar(), args.getCar());
param = param.getCdr();
args = args.getCdr();
}
Node body = new Cons(new Ident("begin"), fun.getCdr().getCdr());
return body.eval(funcEnvironment);
}
public override Node apply(Node args)
{
Environment funcEnv = new Environment(env);
Node temp = fun.getCdr().getCar();
while (temp != Nil.getInstance())
{
funcEnv.define(temp.getCar(), args.getCar());
temp = temp.getCdr();
args = args.getCdr();
}
Node body = new Cons(new Ident("begin"), fun.getCdr().getCdr());
return(body.eval(funcEnv));
}
public override Node eval(Node exp, Environment env)
{
int numArgs = 0;
Node expCdr = exp.getCdr();
while (!expCdr.isNull())
{
numArgs++;
expCdr = expCdr.getCdr();
}
if (numArgs < 2)
{
Console.Error.WriteLine("Error: invalid expression");
return(Nil.getInstance());
}
Node arg1 = exp.getCdr().getCar();
if (numArgs == 2 && arg1.isSymbol())
{
Node val = exp.getCdr().getCdr().getCar();
env.define(arg1, val.eval(env));
return(new StringLit("; no values returned", false));
}
if (arg1.isPair())
{
Node fName = arg1.getCar();
Node fArgs = arg1.getCdr();
Node fBody = exp.getCdr().getCdr();
bool validArgs = verifyArgs(fArgs);
if (fName.isSymbol() && validArgs)
{
Node node = new Cons(new Ident("lambda"), new Cons(fArgs, fBody));
env.define(fName, node.eval(env));
return(new StringLit("; no values returned", false));
}
Console.Error.WriteLine("Error: ill-formed definition");
return(Nil.getInstance());
}
Console.Error.WriteLine("Error: invalid expression");
return(Nil.getInstance());
}
public override Node eval(Environment env, Node args)
{
Node expr1 = args.getCar();
if (args.getCdr().isNull() == true)
{
return(new StringLit("Error: Only 1 argument passed to 'define.'"));
}
else if (args.getCdr().getCdr().isNull() == false)
{
return(new StringLit("Error: Too many arguments passed to 'define.'"));
}
// Is this defining a function?
else if (expr1.isPair() == true)
{
if (expr1.getCar().isSymbol() == true)
{
// Construct the lambda expression
Node formalsAndBody = new Cons(expr1.getCdr(), args.getCdr());
Node lambdaExpr = new Cons(new Ident("lambda"), formalsAndBody);
// define.apply()
return(env.define(expr1.getCar(), lambdaExpr.eval(env)));
}
else
{
return(new StringLit("Error: First argument to 'define' must be a <variable>"));
}
}
else
{
if (expr1.isSymbol() == true)
{
// define.apply()
return(env.define(expr1, args.getCdr().getCar().eval(env)));
}
else
{
return(new StringLit("Error: First argument to 'define' must be a <variable>"));
}
}
}
