public override MatchResult?MatchStep(MatchStack stack, MatchFrame frame, TokenQueue q)
{
if (frame.OrState == OrTermState.Start)
{
// try to match the first sub-production
stack.Push(Prods[0]);
frame.OrState = OrTermState.Match;
frame.OrProdIndex = 0;
frame.OrStartLoc = q.GetLocation();
return(null);
}
else if (frame.OrState == OrTermState.Match)
{
// we have finished matching one of the productions. if it matched, then we're done. if not, move on
// to the next production.
var result = frame.SubResult;
if (result.IsMatch)
{
return(MatchResult.Matched);
}
else if (result.ErrorMessage == null)
{
// no match. rewind to the beginning and retry with the next one.
q.Jump(frame.OrStartLoc);
frame.OrProdIndex++;
if (frame.OrProdIndex >= Prods.Length)
{
// we have exhausted all of the possibilities and none of them matched.
return(MatchResult.NoMatch);
}
stack.Push(Prods[frame.OrProdIndex]);
return(null);
}
else
{
// started to match but mismatched past the point of no return.
return(result);
}
}
else
{
throw new Exception($"Unrecognized state: {frame.OrState}");
}
}
public override MatchResult?MatchStep(MatchStack stack, MatchFrame frame, TokenQueue q)
{
if (frame.OptionalState == OptionalTermState.Start)
{
// try to match the sub-production
stack.Push(Prod);
frame.OptionalState = OptionalTermState.Match;
frame.OptionalStartLoc = q.GetLocation();
return(null);
}
else if (frame.OptionalState == OptionalTermState.Match)
{
// done matching the sub-production
var result = frame.SubResult;
if (result.IsMatch)
{
// the optional term is indeed present.
return(MatchResult.Matched);
}
else if (result.ErrorMessage == null)
{
// it didn't match but wasn't an error. this is fine, but we do have to walk the cursor back to
// where it started since we effectively "matched" zero tokens.
q.Jump(frame.OptionalStartLoc);
return(MatchResult.Matched);
}
else
{
// it started to match but then mismatched past the point of no return. that's an error.
return(result);
}
}
else
{
throw new Exception($"Unrecognized state: {frame.OptionalState}");
}
}
public override MatchResult?MatchStep(MatchStack stack, MatchFrame frame, TokenQueue q)
{
if (frame.ListState == ListTermState.Start)
{
frame.ListState = ListTermState.MatchItem;
stack.Push(ItemProd);
return(null); // -> MatchItem
}
else if (frame.ListState == ListTermState.MatchSeparator)
{
var result = frame.SubResult;
if (result.IsMatch)
{
// we have a separator. now try to match the item following it.
frame.ListState = ListTermState.MatchItem;
stack.Push(ItemProd);
return(null); // -> MatchItem
}
else if (result.ErrorMessage == null)
{
// we didn't find a separator. this list is done. back up to the beginning of where
// the not-separator started and we're done.
q.Jump(frame.ListSeparatorStartLoc);
if (frame.ListCount < Min)
{
return(MatchResult.Error(
$"At least {Min} list item{(Min == 1 ? " is" : "s are")} required, but only " +
$"{frame.ListCount} {(frame.ListCount == 1 ? "was" : "were")} provided. " +
$"Expected list item: {ItemProd.GetExpected()}"));
}
else
{
return(MatchResult.Matched);
}
}
else
{
return(result); // error
}
}
else if (frame.ListState == ListTermState.MatchItem)
{
var result = frame.SubResult;
if (result.IsMatch)
{
// we have an item. is there another?
frame.ListCount++;
if (SeparatorProd == null)
{
// there is no separator, so match the next item
frame.ListState = ListTermState.MatchItem;
frame.ListSeparatorStartLoc = q.GetLocation();
stack.Push(ItemProd);
return(null); // -> MatchItem
}
else
{
// match separator + item
frame.ListState = ListTermState.MatchSeparator;
frame.ListSeparatorStartLoc = q.GetLocation();
stack.Push(SeparatorProd);
return(null); // -> MatchSeparator
}
}
else if (result.ErrorMessage == null)
{
if (frame.ListCount == 0)
{
// the first item might be missing because the list can potentially be optional.
return(Min == 0 ? MatchResult.Matched : MatchResult.NoMatch);
}
else if (SeparatorProd == null)
{
// there's no separator, so eventually we'll end up here when the list ends.
q.Jump(frame.ListSeparatorStartLoc);
if (frame.ListCount < Min)
{
return(MatchResult.Error(
$"At least {Min} list item{(Min == 1 ? " is" : "s are")} required, but only " +
$"{frame.ListCount} {(frame.ListCount == 1 ? "was" : "were")} provided. " +
$"Expected list item: {ItemProd.GetExpected()}"));
}
else
{
return(MatchResult.Matched);
}
}
else
{
// subsequent items must be present because, in the MatchItem state, we've already consumed a
// separator so there must be an item following it.
return(MatchResult.Error($"Expected list item: {ItemProd.GetExpected()}"));
}
}
else
{
return(result); // error
}
}
else
{
throw new Exception($"Unrecognized state: {frame.ListState}");
}
}