On Sat, Mar 27, 2010 at 8:16 PM, Roman Leshchinskiy <rl@cse.unsw.edu.au> wrote:

On 28/03/2010, at 01:36, Jan-Willem Maessen wrote:

> It's worth pointing out that there's a bit of bang-pattern mysticism going on in this conversation (which has not been uncommon of late!). A non-buggy strictness analyzer should expose the strictness of these functions without difficulty.

Actually, rangeJ is lazy in i and rangeK is lazy in i and j. GHC does unbox everything important here but that needs more optimisations than just strictness analysis. You are right, though, that GHC doesn't need bang patterns here.

Quite right, the condition in rangeK that mentions all variables is under another condition:

rangeK :: Int -> Int -> Int -> Int -> Int
rangeK i j k acc
| k < 1000 =
if i * i + j * j + k * k `mod` 7 == 0

...

So we need to apply some constructor specialization as well to notice that i and j are always of the form (Int# i#).

-Jan

Roman