private static AstFor ParseForIn(TokenStream tks)
{
var si = tks.SourceInfo;
tks.Expect(TokenType.For);
var ident = tks.Expect(TokenType.Ident).StringValue;
tks.Expect(TokenType.In);
var @from = ParseExpression(tks);
tks.Expect(TokenType.DotDot);
var to = ParseExpression(tks);
var opTk = tks.Accept(TokenType.Plus, TokenType.Minus);
var updateOp = opTk?.Type ?? TokenType.Plus;
tks.Expect(TokenType.LCurBracket);
var body = ParseBody(tks);
tks.Expect(TokenType.RCurBracket);
var pre = new AstDeclaration(si, ident, null, @from);
var condOp = (updateOp == TokenType.Plus)
? TokenType.LessThanEquals
: TokenType.GreaterThanEquals;
var itrId = new AstIdent(si, ident);
var cond = new AstBinaryOp(si, itrId, condOp, to);
var update_ = new AstBinaryOp(si, itrId, updateOp, new AstNumber(si, 1));
var update = new AstAssign(si, itrId, update_);
return(new AstFor(si, new List <AstNode> {
pre
}, cond, new List <AstExpression> {
update
}, body));
}
private static AstExpression ParseBinaryOpHelper(TokenStream tks, AstExpression lhs, int minPrec)
{
var si = tks.SourceInfo;
var binOps = BinaryOpPrec.Select(kvp => kvp.Key).ToArray();
while (true)
{
var op = tks.Current;
var thisPrec = GetBinOpPrec(op);
if (thisPrec < minPrec)
{
return(lhs);
}
tks.ThrowIfTokenIsNotIn(binOps);
tks.Advance();
var rhs = ParseUnaryOp(tks);
var next = tks.Current;
var nextPrec = GetBinOpPrec(next);
if (thisPrec < nextPrec ||
(thisPrec == nextPrec && IsBinOpRightAssoc(op)))
{
rhs = ParseBinaryOpHelper(tks, rhs, thisPrec + 1);
}
lhs = new AstBinaryOp(si, lhs, op.Type, rhs);
}
}