Then I think hugs and nhc98 are wrong. The report states that the unliterate version of the file is recovered by "taking only those lines beginning with '>', and removing the first character of those lines", which would leave the lines indented by a single space, not two.
This would appear to be an un-remarked change to the Report since version 1.2. That version states that "program lines have the leading '>' replaced by a leading space, to preserve tab alignments". Version 1.3 removed this specification, and the changed specification only appeared in Haskell'98.
I would like to submit it as a bug in the Report - the older specification, as implemented by Hugs and nhc98 makes more sense in conjunction with the layout rule.
I'm inclined to agree. But I'd like to know what the reason for the change in the first place was. GHC's unlit preprocessor converts the tabs to spaces in such a way that they line up after removal of the '>' characters, by the way. Cheers, Simon