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;
}
}
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 "???";
}
}