private Surface.Expr Term()
{
Surface.Expr left = Factor();
int type = lookahead.Type;
switch (type)
{
case SchoolLexer.MUL:
case SchoolLexer.DIV:
Consume();
break;
default:
return(left);
}
Surface.Expr right = Term();
Surface.Expr expr;
switch (type)
{
case SchoolLexer.MUL:
expr = new Surface.Mul(left, right);
break;
case SchoolLexer.DIV:
expr = new Surface.Div(left, right);
break;
default:
throw new ParserException("unreachable code");
}
return(expr);
}
public static void Main(string[] args)
{
var input = "1 * (2 + 3) - 4";
Console.Write("Input:\n {0}\n\n", input);
var lexer = new SchoolLexer(input);
var parser = new SchoolParser(lexer);
Surface.Expr expr = parser.Parse();
Console.WriteLine("Print:");
var printer = new Printer();
printer.Print(expr);
Console.Write("\n\n");
var desugarer = new Desugarer();
Core.Expr coreExpr = desugarer.Desugar(expr);
var evaluator = new Evaluator();
Console.Write("Result:\n{0}\n\n", evaluator.Evaluate(coreExpr));
}
private Surface.Expr Expr()
{
Surface.Expr left = Term();
int type = lookahead.Type;
switch (type)
{
case SchoolLexer.ADD:
case SchoolLexer.SUB:
Consume();
break;
default:
return(left);
}
Surface.Expr right = Expr();
Surface.Expr expr;
switch (type)
{
case SchoolLexer.ADD:
expr = new Surface.Add(left, right);
break;
case SchoolLexer.SUB:
expr = new Surface.Sub(left, right);
break;
default:
throw new ParserException("unreachable code");
}
return(expr);
}
public Core.Expr Desugar(Surface.Expr expr)
{
return(expr.Accept(this));
}
public void Print(Surface.Expr expr)
{
expr.Accept(this);
}
