On Tue, Jan 10, 2006 at 04:44:33PM +0000, Ian Lynagh wrote:
readChunks :: FirstMonad String readChunks = do xs <- get if null xs then return [] else do let (ys, zs) = foo xs put zs rest <- readChunks return (ys ++ rest)
It looks like changing this let to a case fixes this example, but at the time I'd experimented with that there must have been other issues clouding the effect, such as the following. Foo1 (attached) uses large amounts of memory whereas Foo2 (also attached) runs in a little constant space. The difference is only changing this: else do chunk <- case foo xs of (ys, zs) -> do put zs return ys chunks <- readChunks return (chunk ++ chunks) to this: else case foo xs of (ys, zs) -> do put zs chunks <- readChunks return (ys ++ chunks) but I don't have a good feeling for why this should be the case given I'd expect chunk to be forced, and thus the case evaluated, at the same point in Foo1 as the case is evaluated in Foo2. Is this just a case of GHC's optimiser's behaviour depending on subtle source changes, or am I missing something? Thanks Ian