// Woops. This is left-associative. I wanted a right-associative tree.
public static Expression fromString(String s, PrecedenceRule rule)
{
List <Token> tokens = tokenize(s);
// dumpTokens(tokens);
// tokens.Reverse();
return(fromTokens(tokens, rule));
}
public static Expression fromTokens(List <Token> tokens, PrecedenceRule rule)
{
Stack <TokenOrExpression> stack = new Stack <TokenOrExpression>();
while (true)
{
if (tokens.Count == 0 && stack.Count == 1 && stack.Peek()?.Expression != null)
{
return(stack.Pop().Expression);
}
if (stack.Count == 0)
{
stack.Push(new TokenOrExpression(tokens[0]));
tokens.RemoveAt(0);
}
else if (stack.Peek()?.Token is LiteralToken)
{
ulong val = (stack.Pop().Token as LiteralToken).Value;
stack.Push(new TokenOrExpression(new Literal(val)));
}
else if (stack.Peek()?.Token is RparenToken)
{
stack.Pop(); // Rparen
Expression g = new Group(stack.Pop().Expression);
stack.Pop(); // Lparen
stack.Push(new TokenOrExpression(g));
}
else if (stack.Peek()?.Expression != null)
{
bool reduce = true;
if (rule == PrecedenceRule.PlusFirst)
{
int open = 0;
int seen = 0;
foreach (var t in tokens)
{
if (t is LparenToken)
{
open++;
continue;
}
else if (t is RparenToken)
{
if (--open > 0)
{
continue;
}
else if (open < 0)
{
break;
}
}
if (open == 0 && ++seen > 1)
{
break;
}
if (t is BinopToken)
{
BinopToken tok = t as BinopToken;
if (tok.Kind == BinopKind.Plus)
{
reduce = false;
break;
}
}
}
}
Expression e1 = stack.Pop().Expression;
if (reduce && stack.TryPeek(out TokenOrExpression top) && top.Token is BinopToken)
{
BinopToken binop = stack.Pop().Token as BinopToken;
Expression e2 = stack.Pop().Expression;
stack.Push(new TokenOrExpression(new Binop(e1, binop.Kind, e2)));
}
else // Probably Lparen
{
stack.Push(new TokenOrExpression(e1));
stack.Push(new TokenOrExpression(tokens[0]));
tokens.RemoveAt(0);
}
}
