[Haskell] Nested guards?

Bas van Dijk v.dijk.bas at gmail.com
Thu Dec 6 08:08:24 EST 2007

On Dec 6, 2007 9:06 AM, Simon Peyton-Jones <simonpj at microsoft.com> wrote:
> b) the Clean manual says: "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".  That's a pity.  The main point about guards is that failure means "go on to the next
> equation", a semantics that they could have chosen I guess.

I brought this up some time ago on haskell-prime (
http://thread.gmane.org/gmane.comp.lang.haskell.prime/1561 ). One of
the Clean guys mentioned that "the compiler can handle nested-guards
with fall-throughs just fine" and that "The reason that a nested guard
must have a default case is syntactical, otherwise there could be the
dangling-else ambiguity".


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