Bas van Dijk writes (to the haskell-prime list):
The Clean Report[1] is not really clear on that but to my knowledge
nested
guards do not have fall-through semantics.
The report does mention this:
"To ensure that at least one of the alternatives of a nested guard
will be
successful, a nested guarded alternative must always have a
'default case' as
last alternative."
I don't think this explanation is accurate. The reason that a nested
guard must
have a default case is syntactical, otherwise there could be the
dangling-else
ambiguity. If I remember correctly, the compiler can handle nested-
guards with
fall-throughs just fine.
There have been proposals to use the offside rule to resolve the
ambiguity, but
I can't recall if this was implemented.
See <http://mailman.science.ru.nl/pipermail/clean-list/
1997/000175.html> for
some examples.
Cheers,
Ronny Wichers Schreur
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