Talk:Correctness of short cut fusion
If unfoldr would use a lazy pattern match:
unfoldr :: (b -> Maybe (a,b)) -> b -> [a] unfoldr p e = case p e of Nothing -> [] Just ~(x,e') -> x:unfoldr p e'
the left hand side of the example without seq will be the same as the right hand side:
destroy g (unfoldr p e) = g step (unfoldr p e) = case step (unfoldr p e) of Just z -> 0 = case step (case p e of Nothing -> [] Just ~(x,e') -> x:unfoldr p e') of Just z -> 0 = case step (case Just undefined of Nothing -> [] Just ~(x,e') -> x:unfoldr p e') of Just z -> 0 = case step (undefined:unfoldr p undefined) of Just z -> 0 = case Just (undefined,unfoldr p undefined) of Just z -> 0 = 0
--Twanvl 12:18, 13 February 2007 (UTC)