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 ===============================================================================