/// <summary>
/// This method binds names with values, but doesn't allow their usage within expressions
/// that are being bound.
/// </summary>
private Bounce ApplyLetSpecialForm(IExpression expressions, Environment env, Cont cont)
{
var letSpecialForm = expressions as ScmLetSpecialForm;
// Split keys and values in separate lists.
var bindingKeys = new List <IExpression> ();
var bindingValues = new List <IExpression> ();
foreach (var keyValue in letSpecialForm.Bindings)
{
bindingValues.Add(keyValue.Value);
bindingKeys.Add(keyValue.Key);
}
// Evaluate values.
return(() => EvalList(bindingValues, env, evalBindingResults =>
{
var bindingResultsAsList = evalBindingResults as List <IExpression>;
// Create a temporary environment frame that will hold these
// bindings.
var environmentFrame = new EnvironmentFrame();
for (int i = 0; i < bindingKeys.Count; ++i)
{
var bindingName = bindingKeys[i] as ScmSymbol;
var bindingValue = bindingResultsAsList[i];
environmentFrame.Set(bindingName, bindingValue);
}
// Extend the environemnt with these bindings.
var newEnvironment = (new Environment(env)).Extend(environmentFrame);
// Evaluate the body in the new environment.
return EvalList(letSpecialForm.Expressions, newEnvironment, evalResults =>
{
var evalResultsAsList = evalResults as List <IExpression>;
return (Bounce)cont(evalResultsAsList.Last());
});
}));
}
public Environment()
{
// Set up global environment.
var initialFrame = new EnvironmentFrame();
// Numeric operations.
initialFrame.Set(new ScmSymbol("+"), new ScmAddition());
initialFrame.Set(new ScmSymbol("-"), new ScmSubtraction());
initialFrame.Set(new ScmSymbol("*"), new ScmMultiplication());
initialFrame.Set(new ScmSymbol("/"), new ScmDivision());
initialFrame.Set(new ScmSymbol("zero?"), new ScmZeroPredicateProcedure());
initialFrame.Set(new ScmSymbol("odd?"), new ScmOddPredicateProcedure());
initialFrame.Set(new ScmSymbol("even?"), new ScmEvenPredicateProcedure());
initialFrame.Set(new ScmSymbol("quotient"), new ScmQuotientProcedure());
initialFrame.Set(new ScmSymbol("remainder"), new ScmRemainderProcedure());
initialFrame.Set(new ScmSymbol("modulo"), new ScmModuloProcedure());
initialFrame.Set(new ScmSymbol("abs"), new ScmAbsProcedure());
initialFrame.Set(new ScmSymbol("min"), new ScmMinProcedure());
initialFrame.Set(new ScmSymbol("max"), new ScmMaxProcedure());
initialFrame.Set(new ScmSymbol("number?"), new ScmNumberPredicateProcedure());
initialFrame.Set(new ScmSymbol("integer?"), new ScmIntegerPredicateProcedure());
initialFrame.Set(new ScmSymbol("real?"), new ScmRealPredicateProcedure());
// TODO: exact?, inexact?, positive?, negative?,
// sin, cos, sqrt etc.
// True, false and comparison operations.
initialFrame.Set(new ScmSymbol("#t"), ScmTrueValue.Instance);
initialFrame.Set(new ScmSymbol("#f"), ScmFalseValue.Instance);
initialFrame.Set(new ScmSymbol("<"), new ScmLessThan());
initialFrame.Set(new ScmSymbol(">"), new ScmGreaterThan());
initialFrame.Set(new ScmSymbol("="), new ScmEqualTo());
initialFrame.Set(new ScmSymbol("<="), new ScmLessThanOrEqualTo());
initialFrame.Set(new ScmSymbol(">="), new ScmGreaterThanOrEqualTo());
// List procedures.
initialFrame.Set(new ScmSymbol("cons"), new ScmConsProcedure());
initialFrame.Set(new ScmSymbol("list"), new ScmListProcedure());
initialFrame.Set(new ScmSymbol("list?"), new ScmListPredicateProcedure());
initialFrame.Set(new ScmSymbol("null?"), new ScmNullPredicateProcedure());
initialFrame.Set(new ScmSymbol("length"), new ScmLengthProcedure());
initialFrame.Set(new ScmSymbol("list-ref"), new ScmListRefProcedure());
initialFrame.Set(new ScmSymbol("car"), new ScmCarProcedure());
initialFrame.Set(new ScmSymbol("cdr"), new ScmCdrProcedure());
initialFrame.Set(new ScmSymbol("set-car!"), new ScmSetCarProcedure());
initialFrame.Set(new ScmSymbol("set-cdr!"), new ScmSetCdrProcedure());
// Continuation and evaluation procedures.
initialFrame.Set(new ScmSymbol("eval"), new ScmEvalProcedure());
initialFrame.Set(new ScmSymbol("call/cc"), new ScmCallCcProcedure());
initialFrame.Set(new ScmSymbol("call-with-current-continuation"), new ScmCallCcProcedure());
Extend(initialFrame);
}
private Bounce ApplyClosureProcedure(ScmCombination combination, Environment env, Cont cont)
{
//((lambda (b . a) a) 1)
var closure = combination.Procedure as ScmClosure;
var numberOfArguments = closure.ArgumentList.Count;
var operands = new List <IExpression> (combination.Operands);
if (!closure.Dotted && numberOfArguments != operands.Count)
{
throw new EvaluatorException(String.Format("Expecting {0} argument{1}", numberOfArguments, numberOfArguments > 1 ? "s" : ""), combination);
}
else if (closure.Dotted)
{
var numberOfArgumentsButLast = numberOfArguments - 1;
if (numberOfArgumentsButLast > operands.Count)
{
throw new EvaluatorException(String.Format("Expecting at least {0} argument{1}", numberOfArgumentsButLast, numberOfArgumentsButLast > 1 ? "s" : ""), combination);
}
else if (numberOfArgumentsButLast == operands.Count)
{
operands.Add(ScmEmptyList.Instance);
}
else
{
var lastArgument = new ScmPair(operands.TailFrom(numberOfArgumentsButLast));
operands = new List <IExpression> (operands.GetRange(0, numberOfArgumentsButLast));
operands.Add(lastArgument);
}
}
return(() => EvalList(operands, env, evalResults =>
{
var environmentFrame = new EnvironmentFrame();
var evalResultsAsList = evalResults as List <IExpression>;
for (int i = 0; i < closure.ArgumentList.Count; ++i)
{
var argumentName = closure.ArgumentList[i];
var argumentValue = evalResultsAsList[i];
environmentFrame.Set(argumentName, argumentValue);
}
var newEnvironment = (new Environment(closure.Env)).Extend(environmentFrame);
return EvalList(closure.Body.AllButLast(), newEnvironment, bodyEvalResults =>
{
return Eval(closure.Body.Last(), newEnvironment, cont);
});
}));
}
/// <summary>
/// This method binds names with values allowing their usage within expressions
/// that are being bound.
/// </summary>
private Bounce ApplyLetrecSpecialForm(IExpression expression, Environment env, Cont cont)
{
// In comments below we refer to bindings as key-value pairs.
var letRecSpecialForm = expression as ScmLetrecSpecialForm;
// We are going to use a temporary environmental frame, using which we are
// going to define dummy values for each identifier first, and then substitute with
// evaluated ones.
var environmentFrame = new EnvironmentFrame();
// A list of names (keys) that we are going to bind.
var bindingKeys = new List <IExpression> ();
// A list of corresponding values.
var bindingValues = new List <IExpression> ();
// Proccess each pair in the list of bindings, by saving
// them in corresponding lists and assigning
// the unassigned value to each of the identifiers.
foreach (var keyValue in letRecSpecialForm.Bindings)
{
bindingValues.Add(keyValue.Value);
bindingKeys.Add(keyValue.Key);
environmentFrame.Set((ScmSymbol)keyValue.Key, ScmUnassigned.Instance);
}
// Now evaluate each expression (i.e. "value").
return(() => EvalList(bindingValues, env, evalBindingsResult =>
{
var bindingResultsAsList = evalBindingsResult as List <IExpression>;
// Substitute evaluated results.
for (int i = 0; i < bindingKeys.Count; ++i)
{
var bindingName = bindingKeys[i] as ScmSymbol;
var bindingValue = bindingResultsAsList[i];
environmentFrame.Set(bindingName, bindingValue);
}
// Extend the environment with this new frame.
// FIXME: it should "branch" here, and not create a copy of entire environment.
var newEnvironment = (new Environment(env)).Extend(environmentFrame);
// And evalute expressions in the environment with those bindings.
return EvalList(letRecSpecialForm.Expressions, newEnvironment, evalResults =>
{
// FIXME: rewrite this in the same manner as for closure.
var evalResultsAsList = evalResults as List <IExpression>;
return (Bounce)cont(evalResultsAsList.Last());
});
}));
}
/// <summary>
/// Extends the environment by adding a given frame on top of the stack.
/// </summary>
/// <param name="frame"></param>
/// <returns>This environment.</returns>
public Environment Extend(EnvironmentFrame frame)
{
m_Env.Push(frame);
return(this);
}