Hugs did not support lexically scoped type variables then (and
probably doesn't support now).
I may be misremembering, but I think Hugs had them first;-)
http://cvs.haskell.org/Hugs/pages/hugsman/exts.html#sect7.3.3
It is just that Hugs and GHC interpret the language extension
differently (as usual), so it doesn't quite support the same code
in both. That is made worse by differences in other language
features relevant to using this extension. Not to mention that
all of that keeps evolving over time.
Claus
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