On Jun 22, 2009, at 6:38 PM, Ryan Ingram wrote:
Not 100% sure (especially without source/core), but my guess is that
the higher-rank types make the rule unlikely to fire.
Try -ddump-simpl to see the core output, and look for places where you
expect the rule to fire. I suspect you will find that the types of f
and g are not "forall" at that point in the code, but have already
been specialized.
Is there a reason you cannot use this simpler rule?
{-# RULES "transform/tranform" forall f g l. transform f (transform g
l) = transform (g.f) l #-}
Yes, this is the reason:
Inferred type is less polymorphic than expected
Quantified type variable `m' is mentioned in the environment:
f :: (a -> m) -> b -> m (bound at Data/FMList.hs:124:29)
In the first argument of `transform', namely `f'
In the expression: transform f (transform g l)
When checking the transformation rule "transform/transform"
This is the function:
transform :: (forall m. Monoid m => (a -> m) -> (b -> m)) -> FMList b -
> FMList a
transform t l = FM $ \f -> unFM l (t f)
I'll have to clean things up before the core output becomes manageable.
Sjoerd
-- ryan
On Mon, Jun 22, 2009 at 2:41 AM, Sjoerd
Visscher<sjo...@w3future.com> wrote:
Hi all,
I have a rewrite rule as follows:
{-# RULES
"transform/transform" forall (f::forall m. Monoid m => (a -> m) ->
(b -> m))
(g::forall m. Monoid m => (b -> m) ->
(c -> m))
(l::FMList c). transform f (transform g
l) =
transform (g.f) l
#-}
It fires on this code:
print $ transform (. (*2)) (transform (. (+1)) (upto 10))
But it doesn't fire on this code:
print $ map (*2) (map (+1) (upto 10)))
with
map g x = transform (. g) x
and with or without {-# INLINE map #-}.
What am I doing wrong?
--
Sjoerd Visscher
sjo...@w3future.com
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
--
Sjoerd Visscher
sjo...@w3future.com
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
