[Haskell-cafe] rewrite rules

[Simon Peyton-Jones]

| 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

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