Re: [Haskell-cafe] derivation of mapP, a parallel, lazy map

Felipe Lessa wrote:

On Sun, Feb 24, 2008 at 1:45 AM, Dan Zwell wrote:

...

If anybody is curious to see this, the page is http://zwell.net/content/haskell.html#mapP . I would appreciate any criticism, too. I hope somebody finds this helpful.

Have you seen parBuffer? I'd also recommend looking at its source. http://haskell.org/ghc/docs/latest/html/libraries/parallel/Control-Parallel-...

Thanks. parBuffer looks more elegant than what I wrote, though it seems that it performs slightly slower--I assume that pattern matching (x:[]) versus (x:y:[]) (etc.) is faster than recursing and keeping a count of the number of elements left to spark. I tested this with mapP f xs = parBuffer 2 rwhnf $ map f xs (though I had to change the test from doing a few slow operations to doing many fast operations, to see any difference.) Clearly using parBuffer would be a win on machines with lots of CPUs, but is there any reason that I would want to use it instead of the mapP I've already defined? Dan