/// <summary>
/// Returns bound expression for the given symbol.
/// </summary>
/// <param name="sym"></param>
/// <returns></returns>
public IExpression Get(ScmSymbol sym)
{
if (Contains(sym))
{
return(m_Frame[sym.Token.AsString]);
}
return(null);
}
/// <summary>
/// Evaluates a symbol by just looking up in an environment.
/// Signals an error if a symbol cannot be found.
/// </summary>
/// <param name="symbol">A symbol to look up.</param>
/// <param name="env">Environment in which the given symbol will be looked up.</param>
/// <param name="cont">Continuation.</param>
/// <returns>Bounce or null.</returns>
private Bounce EvalSymbol(ScmSymbol symbol, Environment env, Cont cont)
{
var evalResult = env.Get(symbol);
if (evalResult is ScmUnassigned)
{
throw new EvaluatorException(String.Format(UserMessages.SymbolIsUnassigned, symbol.Token.AsString), symbol);
}
return(() => (Bounce)cont(evalResult));
}
/// <summary>
/// Searches for a given symbol all the way down the stack; throws
/// an exception if the symbol cannot be found.
/// </summary>
/// <param name="sym"></param>
/// <returns></returns>
public IExpression Get(ScmSymbol sym)
{
foreach (var env in m_Env)
{
if (env.Contains(sym))
{
return(env.Get(sym));
}
}
throw new EvaluatorException(sym.Token.AsString + " is unbound", sym);
}
/// <summary>
/// Binds a symbol with an expression.
/// </summary>
/// <param name="sym"></param>
/// <param name="value"></param>
public void Set(ScmSymbol sym, IExpression value)
{
if (!Contains(sym))
{
m_Frame.Add(sym.Token.AsString, value);
}
else
{
m_Frame[sym.Token.AsString] = value;
}
}
/// <summary>
/// Updates the binding with the given expression. If the symbol
/// cannot be found in the environment an exception is thrown.
/// </summary>
/// <param name="sym"></param>
/// <param name="value"></param>
public void Set(ScmSymbol sym, IExpression value)
{
foreach (var env in m_Env)
{
if (env.Contains(sym))
{
env.Set(sym, value);
return;
}
}
throw new EvaluatorException(sym.Token.AsString + " is unbound", sym);
}
public ScmSetSpecialForm(ScmSymbol n, IExpression e)
{
m_Name = n;
m_Expression = e;
}
public ScmDefineVarSpecialForm(ScmSymbol n, IExpression e)
{
m_Name = n;
m_Expression = e;
}
public ScmDefineProcSpecialForm(ScmSymbol n, List <ScmSymbol> f, List <IExpression> e, bool dotted)
: base(f, e, dotted)
{
m_ProcedureName = n;
}
/// <summary>
/// Check whether the given symbol is present in this frame.
/// </summary>
/// <param name="sym"></param>
/// <returns></returns>
public bool Contains(ScmSymbol sym)
{
return(m_Frame.ContainsKey(sym.Token.AsString));
}
/// <summary>
/// Creates a new binding on the top-most frame.
/// </summary>
/// <param name="sym"></param>
/// <param name="value"></param>
public void Define(ScmSymbol sym, IExpression value)
{
CurrentFrame.Set(sym, value);
}
/// <summary>
/// This methods analyses the given tokens and produces a list of combinations
/// and expressions that can be parsed further for syntax consistency etc.
/// </summary>
/// <param name="tokens">A list of tokens.</param>
/// <returns>A list of combinations and expressions.</returns>
private static List <IExpression> CombineExpressions(List <Token> tokens)
{
CheckParanthesisBalance(tokens);
var program = new List <IExpression> ();
var eStack = new Stack <IExpression> ();
ScmCombination currentCombination = null;
for (int i = 0; i < tokens.Count; ++i)
{
var token = tokens[i];
if (token is BeginToken)
{
if (currentCombination != null)
{
eStack.Push(currentCombination);
}
currentCombination = new ScmCombination(token);
}
else if (token is EndToken)
{
IExpression cExpr = currentCombination as IExpression;
currentCombination = cExpr as ScmCombination;
if (eStack.Count > 0)
{
var stackExprOnTop = eStack.Peek() as ScmCombination;
stackExprOnTop.Expressions.Add(currentCombination);
currentCombination = eStack.Pop() as ScmCombination;
}
else
{
program.Add(currentCombination);
currentCombination = null;
}
}
else
{
if (token is SymbolToken)
{
IExpression scmSymbol = new ScmSymbol(token);
AddExpression(scmSymbol, currentCombination, program);
}
else if (token is NumberToken)
{
IExpression scmNumber = NumberParser(token as NumberToken);
AddExpression(scmNumber, currentCombination, program);
}
else if (token is StringToken)
{
IExpression scmString = new ScmString(token);
AddExpression(scmString, currentCombination, program);
}
else if (token is DotToken)
{
IExpression scmString = new ScmDotModifier(token);
AddExpression(scmString, currentCombination, program);
}
else if (token is QuoteToken || token is QuasiquoteToken || token is UnquoteToken)
{
IExpression scmQuote = null;
if (token is QuoteToken)
{
scmQuote = new ScmQuoteSpecialForm(null);
}
else if (token is UnquoteToken)
{
scmQuote = new ScmUnquoteSpecialForm(null);
}
else
{
scmQuote = new ScmQuasiquoteSpecialForm(null);
}
AddExpression(scmQuote, currentCombination, program);
}
}
}
return(QuotationSyntacticSugar(program, false));
}
