public void VisitNode(AstNode node)
{
if (node is Statement)
VisitStatement(node as Statement);
else
VisitExpression(node as Expression);
}
public void Optimize()
{
if (Current == null)
throw new InvalidOperationException("Statement or expression tree has not yet been parsed.");
if (Current is Expression)
Current = (Current as Expression).Reduce();
else
(Current as Statement).Optimize();
}
public Statement Parse()
{
// the Game Maker lexer runs before parsing, but we will scan as we are parsing, using l.Scan(),
// implemented in move() and peek(). We will, as in Game Maker, parse completely before executing,
// to catch all compile errors. I've heard Game Maker compiles to byte code, but we will build
// a parse tree of Stmts and Exprs. We return a Stmt node that can be executed by Stmt.Exec().
// Game Maker does all of its parsing during loading, and if there are no errors, caches the
// intermediate representation, which is referenced by the events and scripts.
Statement s;
move();
if (t == TokenKind.OpeningCurlyBrace)
{
s = block(); if (t != TokenKind.Eof) error(Error.ProgramEnds);
return s;
}
s = Statement.Nop;
while (t != TokenKind.Eof)
{
s = new Sequence(s, stmt(), next.line, next.col); // stmt() throws ProgramError
}
Current = s;
return s;
}
/// <summary>
/// This will return a constant 0 if the parser parses an empty string.
/// </summary>
public Expression ParseExpression()
{
move();
if (t == TokenKind.Eof)
return new Constant(0, 0, 0);
Expression e = expr();
if (t != TokenKind.Eof) error(Error.UnexpectedSymbol);
Current = e;
return e;
}
