[Haskell-cafe] rewrite rules

[Ryan Ingram]

Your FMLists are defaulting to Integer, so the rule (which
specifically mentions Int) doesn't apply.  Simon's code doesn't have
this problem because of the explicit signature on "upto"; you could do
the same by limiting "singleton" to Int.

  -- ryan

On Wed, Jun 24, 2009 at 12:44 AM, Sjoerd Visscher<sjoerd at w3future.com> wrote:
> Thanks for looking into this.
>
> Your code does give me 2 firings. But not when I replace [] with FMList. See
> the attached code.
>
>
>
>
>
> Sjoerd
>
> On Jun 23, 2009, at 5:59 PM, Simon Peyton-Jones wrote:
>
>> | 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)))
>>
>> That's odd. It works for me.
>>
>> Specifically, I compiled the attached code with GHC 6.10, and I get two
>> firings of transform/transform.
>>
>> Does that not happen for you?
>>
>> Simon
>>
>> <Rules.hs>
>
> --
> Sjoerd Visscher
> sjoerd at w3future.com
>
>
>
>
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