public static void AddGlobals(SchemeEnvironment e)
{
e.Insert(False.Value, False); e.Insert(True.Value, True); e.Insert(Nil.Value, Nil);
e.Insert("+", new Cell(Plus)); e.Insert("-", new Cell(Minus));
e.Insert("*", new Cell(Multiply)); e.Insert("/", new Cell(Divide));
e.Insert("<", new Cell(LessThan)); e.Insert("<=", new Cell(LessThanEqual));
e.Insert(">", new Cell(GreaterThan)); e.Insert(">=", new Cell(GreaterThanEqual));
e.Insert("=", new Cell(Equal)); e.Insert("==", new Cell(Equal));
e.Insert("print", new Cell(Print));
e.Insert("head", new Cell(Head)); e.Insert("tail", new Cell(Tail));
e.Insert("null?", new Cell(Nullp)); e.Insert("list", new Cell(List));
e.Insert("cons", new Cell(Cons)); e.Insert("append", new Cell(Append));
e.Insert("length", new Cell(Length));
// Add CellType.[Name] definitions
CellType cellType = CellType.SYMBOL;
foreach (var kv in cellType.GetKeyValues <int>())
{
e.Insert("CellType." + kv.Key, new Cell(kv.Value));
}
}
protected Cell InternalEval(Cell x, SchemeEnvironment env)
{
Cell original = x;
++depth;
recurse:
if (debug)
{
if (original != x)
{
Console.WriteLine("{0}) {1} => {2}", new string('-', depth), original, x);
}
else
{
Console.WriteLine("{0}) {1}", new string('-', depth), x);
}
}
++stepCounter;
if (x.Type == CellType.SYMBOL)
{
x = env.Find(x.Value)[x.Value];
goto done;
}
if (x.Type == CellType.NUMBER)
{
goto done;
}
if (x.ListValue.Count == 0)
{
x = StandardRuntime.Nil;
goto done;
}
if (x.ListValue[0].Type == CellType.SYMBOL)
{
Cell sym = x.ListValue[0];
switch ((string)sym)
{
case "quote": // (quote exp)
x = x.ListValue[1];
goto done;
case "if": // (if test conseq [alt])
Cell test = x.ListValue[1];
Cell conseq = x.ListValue[2];
Cell alt = StandardRuntime.Nil;
if (x.ListValue.Count >= 4)
{
alt = x.ListValue[3];
}
Cell testval = Eval(test, env);
Cell final = testval == StandardRuntime.False ? alt : conseq;
x = final;
goto recurse;
case "set!": // (set! var exp) - must exist
x = env.Find(x.ListValue[1].Value)[x.ListValue[1].Value] = Eval(x.ListValue[2], env);
goto done;
case "define": // (define var exp) - creates new
Cell b = Eval(x.ListValue[2], env);
env.Insert(x.ListValue[1].Value, b);
x = b;
goto done;
case "lambda": // (lambda (var*) exp)
x.Type = CellType.LAMBDA;
x.Environment = env;
goto done;
case "macro": // (macro (var*) exp)
x.Type = CellType.MACRO;
x.Environment = env;
goto done;
case "begin": // (begin exp*)
for (int i = 1; i < x.ListValue.Count - 1; ++i)
{
Eval(x.ListValue[i], env);
}
// tail recurse
x = x.ListValue.Last();
goto recurse;
}
}
// (proc exp*)
Cell proc = Eval(x.ListValue[0], env);
List <Cell> exps = new List <Cell>();
if (proc.Type == CellType.MACRO)
{
exps = x.Tail().ListValue;
}
else
{
for (int i = 1; i < x.ListValue.Count; ++i)
{
exps.Add(Eval(x.ListValue[i], env));
}
}
if (proc.Type == CellType.LAMBDA)
{
env = new SchemeEnvironment(proc.ListValue[1].ListValue, exps, proc.Environment);
x = proc.ListValue[2];
goto recurse;
}
else if (proc.Type == CellType.MACRO)
{
SchemeEnvironment env2 = new SchemeEnvironment(proc.ListValue[1].ListValue, exps, proc.Environment);
x = Eval(proc.ListValue[2], env2);
goto recurse;
}
else if (proc.Type == CellType.PROC)
{
x = proc.ProcValue(exps.ToArray());
goto done;
}
else if (proc.Type == CellType.PROCENV)
{
x = proc.ProcEnvValue(exps.ToArray(), env);
goto done;
}
throw new SchemeException("Invalid item in Eval");
done:
if (debug)
{
Console.WriteLine("{0}) {1} => {2} ", new string('-', depth), original, x);
}
--depth;
return(x);
}
