Martin Hofmann wrote: > It is pretty clear, that the following is not a valid Haskell pattern: > > foo (x:x:xs) = x:xs > > My questions is _why_ this is not allowed. IMHO, the semantics should > be > clear: The pattern is expected to succeed, iff 'x' is each time bound > to the same term.
How do you define the "same term"? One natural way of compiling it would be to foo (x:y:xs) | x == y = x:xs but then pattern matching can introduce Eq constraints which some might see as a bit odd. > Isn't this allowed, because this would require a strict evaluation of > the 'x' variables? The translation into == would probably introduce some strictness, for most implementations of Eq. I don't think this is a huge problem in itself. Ganesh =============================================================================== Please access the attached hyperlink for an important electronic communications disclaimer: http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html =============================================================================== _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
