private Stmt ForStatement()
{
Consume(TokenType.LEFT_PAREN, "Expect '(' after 'for'.");
Stmt initializer;
if (Match(TokenType.SEMICOLON))
{
initializer = null;
}
else if (Match(TokenType.VAR))
{
initializer = VarDeclaration();
}
else
{
initializer = ExpressionStatement();
}
Expr condition = null;
if (!Check(TokenType.SEMICOLON))
{
condition = Expression();
}
Consume(TokenType.SEMICOLON, "Expect ';' after loop condition.");
Expr increment = null;
if (!Check(TokenType.RIGHT_PAREN))
{
increment = Expression();
}
Consume(TokenType.RIGHT_PAREN, "Expect ')' after for clauses.");
// This is the for loop body provided by the user
Stmt forLoopBody = Statement();
//////////////// The for loop is rewritten as a while loop. ///////////
//Copy for loop body into a list of while loop statements
List <Stmt> whileLoopStatements = new List <Stmt> {
forLoopBody
};
//If an increment was given, append it to the list of while loop statements
if (increment != null)
{
whileLoopStatements.Add(new Stmt.Expression(increment));
}
//Form the while loop, without the initializer
//Condition is forced to "true" if the for loop had no condition expression
Stmt whileLoop = new Stmt.While(
condition ?? new Expr.Literal(true),
new Stmt.Block(whileLoopStatements)
);
//If no initializer given, just return the while loop.
//Otherwise, insert the initializer just above the while loop
return(initializer == null ? whileLoop : new Stmt.Block(new List <Stmt>
{
initializer,
whileLoop,
}));
}
public MyVoid VisitWhileStmt(Stmt.While stmt)
{
resolve(stmt.condition);
resolve(stmt.body);
return(null);
}