public static Object Cond(Cons args, Environment environment)
{
Cons clauses = args;
while (clauses.Length() > 0)
{
if (clauses.Length() == 1)
{
// This is a default (else) clause, so just execute it
return(Runtime.Eval(clauses.First(), environment));
}
if (clauses.Length() >= 2)
{
if (Conversions.ObjectToBoolean(Runtime.Eval(clauses.First(), environment)))
{
return(Runtime.Eval(clauses.Second(), environment));
}
else
{
clauses = (Cons)clauses.Cddr();
}
}
}
return(null);
}
public static Object And(Cons args, Environment environment)
{
foreach (Object item in args)
{
if (Conversions.ObjectToBoolean(Runtime.Eval(item, environment)) == false)
{
return(false);
}
}
return(true);
}
public static Object While(Cons args, Environment environment)
{
object test;
while ((Conversions.ObjectToBoolean(test = Runtime.Eval(args.First(), environment))))
{
foreach (object item in (Cons)args.Rest())
{
Runtime.Eval(item, environment);
}
}
return(test);
}
public static Object For(Cons args, Environment environment)
{
Environment localEnvironment = new Environment(environment);
Runtime.Eval(args.First(), localEnvironment);
object test;
while ((Conversions.ObjectToBoolean(test = Runtime.Eval(args.Second(), localEnvironment))))
{
foreach (object item in (Cons)args.Cdddr())
{
Runtime.Eval(item, localEnvironment);
}
Runtime.Eval(args.Third(), localEnvironment);
}
return(test);
}
public static Object If(Cons args, Environment environment)
{
if (Conversions.ObjectToBoolean(Runtime.Eval(args.First(), environment)))
{
// Evaluate the then part
return(Runtime.Eval(args.Second(), environment));
}
else
if (args.Length() > 2)
{
// Evaluate the optional else part
return(Runtime.Eval(args.Third(), environment));
}
else
{
return(null);
}
}
public static Object Not(Cons args, Environment environment)
{
return(!(Conversions.ObjectToBoolean(args.First())));
}