I don't really understand your purpose. There are many ways to write code that GHC is good at optimizing, but there are far fewer ways to write code that will compile to non-allocating loops without optimization. Heck, without the worker-wrapper transformation demand analysis enables, you can't even get a non-allocating counter without unboxing by hand and using primops for arithmetic. On Tue, Sep 4, 2018, 1:00 PM Johannes Waldmann < johannes.waldmann@htwk-leipzig.de> wrote:
Dear Cafe (again),
I was trying to write
sum $ map (^ 2) $ [ 1 :: Int .. 10^8 ]
in a list-free style
getSum $ foldMap (Sum . (^ 2)) $ [ 1 :: Int .. 10^8 ]
This avoids building an intermediate list (of squares) but it will allocate, since foldMap uses foldr (by default, and it's not overridden for lists)
The conclusion would be: not to use lists at all. Which will be the point of my talk anyway.
But here, we get a list from enumFromTo. Can we avoid that?
Let's try: we just reify enumFromTo
data Enumerator a = Enumerator {from :: a, to :: a}
we have this for decades, it is called (a,a) in Data.Ix, and then
instance Foldable Enumerator where ...
Oh no, foldMap (and others) would need an Enum constraint!
- J
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On Sep 4, 2018 1:00 PM, "Johannes Waldmann" < johannes.waldmann@htwk-leipzig.de> wrote: Dear Cafe (again), I was trying to write sum $ map (^ 2) $ [ 1 :: Int .. 10^8 ] in a list-free style getSum $ foldMap (Sum . (^ 2)) $ [ 1 :: Int .. 10^8 ] This avoids building an intermediate list (of squares) but it will allocate, since foldMap uses foldr (by default, and it's not overridden for lists) The conclusion would be: not to use lists at all. Which will be the point of my talk anyway. But here, we get a list from enumFromTo. Can we avoid that? Let's try: we just reify enumFromTo data Enumerator a = Enumerator {from :: a, to :: a} we have this for decades, it is called (a,a) in Data.Ix, and then instance Foldable Enumerator where ... Oh no, foldMap (and others) would need an Enum constraint! - J _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.