Any chance you could make a standalone example demonstrating the problem? ie
one or two modules with suitable definitions, perhaps some stubs. ({-# NOINLINE
#-} is useful for the stubs.) Not only does that make it easier to identify
what's going wrong, but it also means we can add it to the regression suite (if
there is a bug) to ensure it doesn't happen again.
Simon
| -----Original Message-----
| From: [email protected] [mailto:[email protected]] On
Behalf Of
| Simon Meier
| Sent: 11 June 2011 14:44
| To: [email protected]
| Subject: Debugging non-firing rewrite rules
|
| Hi,
|
| there's quite some material on how to debug/track rewrite rules that
| do fire. However, I couldn't find information about how to find out
| what is wrong with a rule that supposedly should, but actually doesn't
| fire. Concretely, I would like to add a rewrite rule that converts
|
| mconcat . map (fromWrite w)
|
| to
|
| fromWriteList w
|
| The relevant definitions and types are:
|
| mconcat = foldr append empty
| append :: Builder -> Builder -> Builder
| empty :: Builder
| fromWrite :: Write a -> a -> Builder
| fromWriteList :: Write a -> [a] -> Builder
|
| The rewrite rule that I tried is
|
| "foldr/fromWrite" forall w.
| foldr (\x b -> append (fromWrite w x) b) empty = fromWriteList w
|
| combined with {-# INLINE [1] #-} anotations on the `append`, `empty`,
| `fromWrite` and `fromWriteList`. However, the rule doesn't fire for a
| definition like
|
| word8s :: [Word8] -> Builder
| word8s = mconcat . map (fromWrite writeWord8)
|
| I suspect that the foldr/build fusion rules are interacting. However,
| I don't know how this interaction looks like. Is there a way to track
| all simplifications of `word8s` in all phases? If there was, then I
| could formulate my rule such that it is reduced with respect to the
| other rewriting rules. Then, the interaction should work out.
|
| thanks for your help,
| Simon
|
| PS: The above definitions are part of the builder for the bytestring
| package [1] and my experiment on rule firings can be found here [2].
|
| [1] https://github.com/meiersi/bytestring
| [2]
|
https://github.com/meiersi/bytestring/blob/master/tests/builder/WriteListFusion.hs
|
| _______________________________________________
| Cvs-ghc mailing list
| [email protected]
| http://www.haskell.org/mailman/listinfo/cvs-ghc
_______________________________________________
Cvs-ghc mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/cvs-ghc
