private static Expression ParseApplicationExpression(IEnumerator<Token> tokens, SymbolTable table)
{
ApplicationExpression result = null;
while (true)
{
var expression = ParsePrimaryExpression(tokens, table);
if (expression == null)
break;
if (result == null)
result = new ApplicationExpression { Left = expression, Right = null };
else if (result.Right == null)
result.Right = expression;
else
result = new ApplicationExpression { Left = result, Right = expression };
}
if (result == null)
throw new Exception("expression expected");
if (result.Right == null)
return result.Left; // PrimaryExpression
else
return result;
}
public SymbolTable(SymbolTable parent)
{
_parent = parent;
if (parent != null)
{
_bottom = parent._bottom;
}
else
{
_bottom = this;
_boundSymbols = new Dictionary<int, string>();
_builtinNames = new BuiltinNames(this);
}
}
public static Expression Parse(string text, SymbolTable table)
{
var tokens = Tokenize(text);
var enumerator = tokens.GetEnumerator();
if (!enumerator.MoveNext())
throw new Exception("token list must not be empty");
var expression = ParseExpression(enumerator, table);
if (enumerator.Current.Type != TokenType.Eof)
throw new Exception("unexpected token '" + enumerator.Current.Text + "'");
return expression;
}
public static Expression ConvertToBuiltin(Expression expression, SymbolTable table)
{
// _Bool
bool boolValue;
if (RecognizeBool(expression, out boolValue))
return table.BuiltinNames.CreateBool(boolValue);
// _Integer
int integerValue;
if (RecognizeInteger(expression, out integerValue))
return table.BuiltinNames.CreateInteger(integerValue);
// _List
BuiltinList listValue;
if (RecognizeList(expression, out listValue))
return table.BuiltinNames.CreateList(listValue);
// _Pair
BuiltinPair pairValue;
if (RecognizePair(expression, out pairValue))
return table.BuiltinNames.CreatePair(pairValue);
// _Maybe
Expression maybeValue;
if (RecognizeMaybe(expression, out maybeValue))
return table.BuiltinNames.CreateMaybe(maybeValue);
return null;
}
public BuiltinNames(SymbolTable table)
{
int x = table.Register("x");
int y = table.Register("y");
_names = new Dictionary<string, Expression>();
_names.Add("_True", CreateBool(true));
_names.Add("_False", CreateBool(false));
_names.Add("_Zero", CreateInteger(0));
_names.Add("_Successor", new AbstractionExpression
{
Left = new SymbolRef(x),
Right = new BuiltinExpression
{
Left = new BoundSymbolExpression { Symbol = new SymbolRef(x) },
Right = null,
Evaluate = _SuccessorEvaluate
}
});
_names.Add("_Null", new FreeSymbolExpression { Name = "_List", Tag = null, Display = _ListDisplay });
_names.Add("_Nothing", new FreeSymbolExpression { Name = "_Maybe", Tag = null, Display = _MaybeDisplay });
}
private static Expression ParseAbstractionExpression(IEnumerator<Token> tokens, SymbolTable table)
{
if (tokens.Current.Type == TokenType.Symbol && tokens.Current.Text == "\\")
{
tokens.MoveNext();
var bindList = ParseBindList(tokens);
if (tokens.Current.Type == TokenType.Symbol && tokens.Current.Text == ".")
{
SymbolTable childTable = new SymbolTable(table);
var bindIdList = new List<int>(bindList.Count);
for (int i = 0; i < bindList.Count; i++)
bindIdList.Add(childTable.Register(bindList[i]));
tokens.MoveNext();
var rest = ParseAbstractionExpression(tokens, childTable);
Expression rhs = rest;
for (int i = 0; i < bindIdList.Count; i++)
{
rhs = new AbstractionExpression { Left = new SymbolRef(bindIdList[bindIdList.Count - i - 1]), Right = rhs };
}
return rhs;
}
else
{
throw new Exception("'.' expected");
}
}
else
{
return ParseApplicationExpression(tokens, table);
}
}
private static Expression ParsePrimaryExpression(IEnumerator<Token> tokens, SymbolTable table)
{
if (tokens.Current.Type == TokenType.Symbol && tokens.Current.Text == "(")
{
tokens.MoveNext();
var expression = ParseExpression(tokens, table);
if (tokens.Current.Type == TokenType.Symbol && tokens.Current.Text == ")")
{
tokens.MoveNext();
return expression;
}
else
{
throw new Exception("')' expected");
}
}
else if (tokens.Current.Type == TokenType.Id)
{
string name = tokens.Current.Text;
int id = table.Lookup(name);
tokens.MoveNext();
if (id != 0)
return new BoundSymbolExpression { Symbol = new SymbolRef(id) };
else
return new FreeSymbolExpression { Name = name };
}
else
{
return null;
}
}
private static Expression ParseExpression(IEnumerator<Token> tokens, SymbolTable table)
{
return ParseAbstractionExpression(tokens, table);
}
private string _PairDisplay(Expression expression, SymbolTable table)
{
var freeSymbol = (FreeSymbolExpression)expression;
BuiltinPair pair = (BuiltinPair)freeSymbol.Tag;
StringBuilder sb = new StringBuilder();
sb.Append("<" + freeSymbol.Name + ">");
Expression displayExpression;
// First
displayExpression = Evaluator.ConvertToBuiltin(pair.First, table);
if (displayExpression == null)
displayExpression = pair.First;
sb.Append("(" + Evaluator.ConvertToString(displayExpression, table) + ")");
// Second
displayExpression = Evaluator.ConvertToBuiltin(pair.Second, table);
if (displayExpression == null)
displayExpression = pair.Second;
sb.Append("(" + Evaluator.ConvertToString(displayExpression, table) + ")");
return sb.ToString();
}
private string _MaybeDisplay(Expression expression, SymbolTable table)
{
var freeSymbol = (FreeSymbolExpression)expression;
Expression value = (Expression)freeSymbol.Tag;
StringBuilder sb = new StringBuilder();
sb.Append("<" + freeSymbol.Name + ">");
Expression displayExpression;
if (value != null)
{
displayExpression = Evaluator.ConvertToBuiltin(value, table);
if (displayExpression == null)
displayExpression = value;
sb.Append("(" + Evaluator.ConvertToString(displayExpression, table) + ")");
}
else
{
sb.Append("Nothing");
}
return sb.ToString();
}
private string _ListDisplay(Expression expression, SymbolTable table)
{
var freeSymbol = (FreeSymbolExpression)expression;
BuiltinList list = (BuiltinList)freeSymbol.Tag;
StringBuilder sb = new StringBuilder();
sb.Append("<" + freeSymbol.Name + ">");
if (list == null)
{
sb.Append("Null");
}
else
{
do
{
var displayExpression = Evaluator.ConvertToBuiltin(list.First, table);
if (displayExpression == null)
displayExpression = list.First;
sb.Append("(" + Evaluator.ConvertToString(displayExpression, table) + ")");
list = list.Second;
} while (list != null);
}
return sb.ToString();
}
private string _IntegerDisplay(Expression expression, SymbolTable table)
{
var freeSymbol = (FreeSymbolExpression)expression;
return "<" + freeSymbol.Name + ">" + ((int)freeSymbol.Tag).ToString();
}
public static string ConvertToString(Expression expression, SymbolTable table)
{
if (expression is BoundSymbolExpression)
{
var boundSymbol = (BoundSymbolExpression)expression;
return table.Lookup(boundSymbol.Symbol.Symbol);
}
else if (expression is FreeSymbolExpression)
{
var freeSymbol = (FreeSymbolExpression)expression;
if (freeSymbol.Display != null)
return freeSymbol.Display(freeSymbol, table);
return freeSymbol.Name;
}
else if (expression is AbstractionExpression)
{
var abstraction = (AbstractionExpression)expression;
return "\\" + table.Lookup(abstraction.Left.Symbol) + "." + ConvertToString(abstraction.Right, table);
}
else if (expression is ApplicationExpression)
{
var application = (ApplicationExpression)expression;
string left;
string right;
if (application.Left is AbstractionExpression)
left = "(" + ConvertToString(application.Left, table) + ")";
else
left = ConvertToString(application.Left, table);
if ((application.Right is AbstractionExpression) || (application.Right is ApplicationExpression))
right = "(" + ConvertToString(application.Right, table) + ")";
else
right = ConvertToString(application.Right, table);
return left + " " + right;
}
else if (expression is LazyExpression)
{
var lazy = (LazyExpression)expression;
return "<#" + lazy.Id.ToString() + ">";
}
else if (expression is BuiltinExpression)
{
var builtin = (BuiltinExpression)expression;
if (builtin.Display != null)
return builtin.Display(expression, table);
string left = builtin.Left != null ? ConvertToString(builtin.Left, table) : "";
string right = builtin.Right != null ? ConvertToString(builtin.Right, table) : "";
if (right == "")
return "<BUILTIN>(" + left + ")";
else
return "<BUILTIN>(" + left + ")(" + right + ")";
}
else
{
return "???";
}
}
