Re: [Haskell-cafe] lazy evaluation is not complete

On Mon, Feb 9, 2009 at 10:50 PM, Iavor Diatchki wrote:

I 0 * _ = I 0 I x * I y = I (x * y)

Note that (*) is now non-commutative (w.r.t. _|_). Of course, that's what we need here, but it means that the "obviously correct" transformation of

foo x = if x == 0 then 0 else foo (x - 1) * foo (x + 1)

into foo' x = if x == 0 then 0 else foo' (x + 1) * foo' (x - 1) is *not* in fact correct. --Max