Hi, is this a known bug or feature of GHC (7.4.1, 7.6.3)?: I got a looping behavior in one of my programs and could not explain why. When I rewrote an irrefutable let with guards to use a case instead, the loop disappeared. Cut-down: works = case Just 1 of { Just x | x > 0 -> x } loops = let Just x | x > 0 = Just 1 in x works returns 1, loops loops. If x is unused on the rhs, the non-termination disappears. works' = let Just x | x > 0 = Just 1 in 42 Is this intended by the Haskell semantics or is this a bug? I would have assumed that non-recursive let and single-branch case are interchangeable, but apparently, not... Cheers, Andreas -- Andreas Abel <>< Du bist der geliebte Mensch. Theoretical Computer Science, University of Munich Oettingenstr. 67, D-80538 Munich, GERMANY andreas.abel@ifi.lmu.de http://www2.tcs.ifi.lmu.de/~abel/