public static SchemeObject Evaluate(Expression expression, SchemeEnvironment environment)
{
Stack<ContinuationFrame> stack = new Stack<ContinuationFrame>();
SchemeObject value = null;
evaluate:
switch (expression.NodeType)
{
case NodeType.Assignment:
{
Assignment assignment = (Assignment)expression;
stack.Push(new AssignmentContinuation(assignment.Destination.Symbol, assignment.IsDefinition, environment));
expression = assignment.Source;
goto evaluate;
}
case NodeType.Conditional:
{
Conditional conditional = (Conditional)expression;
stack.Push(new ConditionalContinuation(conditional.Consequent, conditional.Alternate, environment));
expression = conditional.Test;
goto evaluate;
}
case NodeType.LambdaExpression:
{
value = new Closure(environment, (Lambda)expression);
goto apply;
}
case NodeType.Literal:
{
value = ((Literal)expression).Value;
goto apply;
}
case NodeType.ProcedureCall:
{
ProcedureCall procedureCall = (ProcedureCall)expression;
stack.Push(new ProcedureContinuation(procedureCall.Arguments, environment));
expression = procedureCall.Procedure;
goto evaluate;
}
case NodeType.Sequence:
{
Sequence sequence = (Sequence)expression;
stack.Push(new SequenceContinuation(sequence, environment));
goto apply;
}
case NodeType.Variable:
{
Variable variable = (Variable)expression;
value = environment.GetValue(variable.Symbol);
goto apply;
}
default:
{
System.Diagnostics.Debug.Assert(false);
throw new InvalidOperationException();
}
}
apply:
if (stack.Count == 0)
return value;
ContinuationFrame frame = stack.Pop();
environment = frame.Environment;
switch (frame.Kind)
{
case ContinuationKind.Assignment:
{
AssignmentContinuation assignmentFrame = (AssignmentContinuation)frame;
environment.SetValue(assignmentFrame.Destination, value, assignmentFrame.IsDefinition);
value = SchemeVoid.Instance;
goto apply;
}
case ContinuationKind.Procedure:
{
ProcedureContinuation procedureFrame = (ProcedureContinuation)frame;
ReadOnlyCollection<Expression> arguments = procedureFrame.Arguments;
Procedure procedure = value as Procedure;
if (procedure == null)
throw InvalidSyntaxException.Format("Error: {0} is not a procedure", value.PrettyPrint());
stack.Push(new ArgumentsContinuation(procedure, arguments, environment));
if (arguments.Count == 0)
goto apply;
expression = arguments[0];
goto evaluate;
}
case ContinuationKind.Sequence:
{
SequenceContinuation sequenceFrame = (SequenceContinuation)frame;
Sequence sequence = sequenceFrame.Sequence;
int index = sequenceFrame.Index++;
if (index < sequence.Expressions.Count - 1)
stack.Push(sequenceFrame);
expression = sequence.Expressions[index];
goto evaluate;
}
case ContinuationKind.Conditional:
{
ConditionalContinuation testFrame = (ConditionalContinuation)frame;
if (value != SchemeBoolean.False)
{
expression = testFrame.Consequent;
goto evaluate;
}
if (testFrame.Alternate != null)
{
expression = testFrame.Alternate;
goto evaluate;
}
value = SchemeVoid.Instance;
goto apply;
}
case ContinuationKind.Arguments:
{
ArgumentsContinuation argumentsFrame = (ArgumentsContinuation)frame;
int index = argumentsFrame.Index++;
if (index < argumentsFrame.Arguments.Count)
{
argumentsFrame.EvaluatedArguments[index] = value;
}
if (argumentsFrame.Index < argumentsFrame.Arguments.Count)
{
stack.Push(argumentsFrame);
expression = argumentsFrame.Arguments[argumentsFrame.Index];
goto evaluate;
}
Primitive primitive = argumentsFrame.Procedure as Primitive;
if (primitive != null)
{
value = primitive.Callback(argumentsFrame.EvaluatedArguments);
goto apply;
}
Closure closure = (Closure)argumentsFrame.Procedure;
expression = closure.Body;
environment = BuildCallEnvironment(argumentsFrame.EvaluatedArguments, closure);
goto evaluate;
}
default:
{
Debug.Assert(false);
throw new InvalidOperationException();
}
}
}
internal ConditionalContinuation(Expression consequent, Expression alternate, SchemeEnvironment environment)
: base(environment, ContinuationKind.Conditional)
{
this.Consequent = consequent;
this.Alternate = alternate;
}
internal ProcedureCall(Expression procedure, IList<Expression> arguments)
{
this.procedure = procedure;
this.arguments = new ReadOnlyCollection<Expression>(arguments);
}
public Assignment(Variable destination, Expression source, bool isDefinition)
{
this.destination = destination;
this.source = source;
this.isDefinition = isDefinition;
}
public Conditional(Expression test, Expression consequent, Expression alternate)
{
this.test = test;
this.consequent = consequent;
this.alternate = alternate;
}
public Lambda(Formals formals, Expression body)
{
this.formals = formals;
this.body = body;
}