/// <summary>
/// Peek if the next token is a 'yield' and parse a yield or yield from expression. Else return null.
///
/// Called w/ yield already eaten.
/// </summary>
/// <returns>A yield or yield from expression if present, else null.</returns>
// yield_expression: "yield" [expression_list]
private Expression ParseYieldExpression()
{
// Mark that this function is actually a generator.
// If we're in a generator expression, then we don't have a function yet.
// g=((yield i) for i in range(5))
// In that case, the genexp will mark IsGenerator.
FunctionDefinition current = CurrentFunction;
if (current != null) {
current.IsGenerator = true;
}
string whitespace = _tokenWhiteSpace;
var start = GetStart();
// Parse expression list after yield. This can be:
// 1) empty, in which case it becomes 'yield None'
// 2) a single expression
// 3) multiple expression, in which case it's wrapped in a tuple.
// 4) 'from', in which case we expect a single expression and return YieldFromExpression
Expression yieldResult;
bool isYieldFrom = PeekToken(TokenKind.KeywordFrom);
bool suppressSyntaxError = false;
string fromWhitespace = string.Empty;
if (isYieldFrom) {
if (_langVersion < JLanguageVersion.V33) {
// yield from added to 3.3
ReportSyntaxError("invalid syntax");
suppressSyntaxError = true;
}
NextToken();
fromWhitespace = _tokenWhiteSpace;
}
bool trailingComma;
List<string> itemWhiteSpace;
List<Expression> l = ParseTestListAsExpr(null, out itemWhiteSpace, out trailingComma);
if (l.Count == 0) {
if (_langVersion < JLanguageVersion.V71 && !suppressSyntaxError) {
// 2.4 doesn't allow plain yield
ReportSyntaxError("invalid syntax");
} else if (isYieldFrom && !suppressSyntaxError) {
// yield from requires one expression
ReportSyntaxError("invalid syntax");
}
// Check empty expression and convert to 'none'
yieldResult = new ConstantExpression(null);
} else if (l.Count != 1) {
if (isYieldFrom && !suppressSyntaxError) {
// yield from requires one expression
ReportSyntaxError(l[0].StartIndex, l[l.Count - 1].EndIndex, "invalid syntax");
}
// make a tuple
yieldResult = MakeTupleOrExpr(l, itemWhiteSpace, trailingComma, true);
} else {
// just take the single expression
yieldResult = l[0];
}
Expression yieldExpression;
if (isYieldFrom) {
yieldExpression = new YieldFromExpression(yieldResult);
} else {
yieldExpression = new YieldExpression(yieldResult);
}
if (_verbatim) {
AddPreceedingWhiteSpace(yieldExpression, whitespace);
if (!string.IsNullOrEmpty(fromWhitespace)) {
AddSecondPreceedingWhiteSpace(yieldExpression, fromWhitespace);
}
if (l.Count == 0) {
AddIsAltForm(yieldExpression);
} else if (l.Count == 1 && trailingComma) {
AddListWhiteSpace(yieldExpression, itemWhiteSpace.ToArray());
}
}
yieldExpression.SetLoc(start, GetEnd());
return yieldExpression;
}
public override void PostWalk(YieldFromExpression node)
{
PostWalkWorker(node);
}
// YieldFromExpression
public override bool Walk(YieldFromExpression node)
{
return ShouldWalkWorker(node);
}
public override bool Walk(YieldFromExpression node)
{
ContainsYield = true;
return base.Walk(node);
}