On Thu, 18 Sep 2003 20:16:33 +0200
Juanma Barranquero
Extremely-newbie questions:
Is there any way to know if a list is finite or infinite, other than doing:
length l
and waiting forever? :)
In Haskell 98, no. With a slightly impure extension (observable sharing) sometimes but in general, no. The only infinity you need to recognize is omega and that's just an infinite (cyclic) list of whatevers. So you -could- use observable sharing for this, but there isn't much point to it, just use a data structure that says, "an infinity of x". The simplest thing I would think of is to follow the arithmetic operation exactly. data SN = Zero | Up | Down | SN :+: SN | SN :*: SN | SN :^: SN | Omega SN omega = Omega Up iota = Up :+: Omega Down twoThirds = Omega (Up :+: Down) twoOmega = Omega Up :+: Omega Up omegaSquared = Omega Up :*: Omega Up omegaToTheOmega = Omega Up :^: Omega Up