[Haskell-cafe] elem of infinite set of tuple

[David Roundy]

On Fri, May 16, 2008 at 07:58:40AM -0400, Dan Doel wrote:
> On Friday 16 May 2008, leledumbo wrote:
> > I don't know how Haskell should behave on this. Consider this function:
> > elemOf (x,y) = (x,y) `elem` [ (a,b) | a <- [0..], b <- [0..] ]
> 
> FYI: The control-monad-omega package on hackage.haskell.org can handle this 
> sort of thing (liberties taken with ghci formatting):
> 
> Prelude> :m + Control.Monad.Omega
> Prelude Control.Monad.Omega>
>   (1,1) `elem` runOmega (do x <- each [0..] ; y <- each [0..] ; return (x,y))
> True
> Prelude Control.Monad.Omega>
> 
> It does breadth-first instead of depth-first search.

You could also just use [ (b,a-b) | a <- [0..], b <- [0..a]]

David