/// <summary>
/// Determines whether the environment contains a definition for
/// a variable with the given symbol
/// </summary>
/// <param name="symbol"></param>
/// <returns>True or false</returns>
public bool Contains(Symbol symbol)
{
if (hashtable.ContainsKey(symbol))
return true;
if (previousEnvironment != null)
return previousEnvironment.Contains(symbol);
return false;
}
/// <summary>
/// Returns a symbol given its name. If necessary the symbol is
/// created and interned.
/// </summary>
/// <param name="name"></param>
/// <returns></returns>
public static Symbol FromName(string name)
{
name = name.ToLower();
Symbol symbol = (Symbol)symbolTable[name];
if(symbol == null)
{
symbol = new Symbol(name);
symbolTable.Add(name, symbol);
}
return symbol;
}
/// <summary>
/// Asssigns value to a local variable symbol in this
/// local environment (irrespective of whether symbol
/// is defined in any parent environments).
/// </summary>
public object AssignLocal(Symbol symbol, object value)
{
hashtable[symbol] = value;
return value;
}
/// <summary>
/// Returns the environment in which a given variable is defined, or null
/// </summary>
private Environment GetEnvironment(Symbol symbol)
{
if (hashtable.ContainsKey(symbol))
return this;
if (previousEnvironment == null)
return null;
return previousEnvironment.GetEnvironment(symbol);
}
/// <summary>
/// Sets a variable with given symbol to a given value
/// </summary>
public object Set(Symbol symbol, object value)
{
if ((hashtable.ContainsKey(symbol)) || (previousEnvironment == null))
return this.AssignLocal(symbol, value);
return previousEnvironment.Set(symbol, value);
}
public object GetValue(Symbol symbol)
{
if (hashtable.ContainsKey(symbol))
{
return hashtable[symbol];
}
if (previousEnvironment != null)
{
return previousEnvironment.GetValue(symbol);
}
throw new LSharpException("Reference to undefined identifier: " + symbol.Name,this);
}
/// <summary>
/// Sets a variable with given symbol to a given value
/// </summary>
/// <param name="symbol"></param>
/// <param name="value"></param>
/// <returns></returns>
public object Assign(Symbol symbol, object value)
{
Environment environment = GetEnvironment(symbol);
if (environment == null)
environment = this;
return environment.AssignLocal(symbol, value);
}
public object GetValue(Symbol symbol)
{
object o = hashtable[symbol];
if ((o == null) && (previousEnvironment != null))
o = previousEnvironment.GetValue(symbol);
return o;
}
public static bool Bound(Symbol symbol, Environment environment)
{
if (environment.Contains(symbol))
return true;
else
return false;
}
/// <summary>
/// Binds the given symbol to the given value in the given
/// environment
/// </summary>
public static object VarSet(Symbol symbol, Object value, Environment environment)
{
environment.Set(symbol, value);
return value;
}
/// <summary>
/// Returns the value that symbol is bound to in the
/// given environment
/// </summary>
public static object VarRef(Symbol symbol, Environment environment)
{
object value = environment.GetValue(symbol);
return value;
}
public static Expression CompileVarRef(Symbol symbol)
{
return Expression.Call(null, varRefMethodInfo, Expression.Constant(symbol), environmentParameter);
}
public static string GenerateAssignLocal(Symbol s, object value, LSharp.Environment environment)
{
if (environment.Contains(s))
{
string ns = MakeUnique(s.Name);
environment.AssignLocal(s, ns);
if (value is string)
{
return string.Format(@"{1}
object {0} = retval;", ns, value) + NewLine;
}
else
{
return string.Format(@"{2} {0} = {1};",
ns, value, value.GetType()) + NewLine;
}
}
else
{
environment.AssignLocal(s, s.Name);
if (value is string)
{
return string.Format(@"{1}
object {0} = retval;", s.Name, value) + NewLine;
}
else
{
return string.Format(@"{2} {0} = {1};", s.Name, value, value.GetType()) + NewLine;
}
}
}
public static string GenerateAssign(Symbol s, object value, LSharp.Environment environment)
{
if (environment.Contains(s))
{
object sn = environment.GetValue(s);
return string.Format(@"{1}
{0} = retval;",
sn, value) + NewLine;
}
else
{
environment.Assign(s, s.Name);
return string.Format(@"{1}
object {0} = retval;",
s.Name, value) + NewLine;
}
}