Thanks, Simon. I'll keep poking around.
On Thu, May 8, 2014 at 12:54 AM, Simon Peyton Jones <[email protected]>wrote: > Yes, that’s right: simplCast is the guy. I can’t explain why it’s not > working for you, though > > > > Simon > > > > *From:* [email protected] [mailto:[email protected]] *On > Behalf Of *Conal Elliott > *Sent:* 08 May 2014 04:19 > *To:* Simon Peyton Jones > *Cc:* [email protected] > *Subject:* Re: Simplifying casts and beta-reduction > > > > I'm still sorting through how to optimize these almost-beta-redexes in the > form `((\ x -> u) |> co) v`, shifting coercions to enable beta-reduction > (as described in section 3.1 of "Evidence normalization"). Is it done by > `simplCast` (with help from `simplCoercion`), as called indirectly from > `simplifyExpr` in `SimplCore`? I think I'm now calling `simplifyExpr` from > HERMIT but I'm not getting the cast-shifting I'm looking for. > > -- Conal > > > > On Wed, May 7, 2014 at 1:02 PM, Conal Elliott <[email protected]> wrote: > > Very useful, indeed! Exactly what I was looking for. Thanks, Simon. Now > I've read the evidence normalization and the deferred types paper, and I > have a much better understanding of what's going on. > > -- Conal > > > > On Wed, May 7, 2014 at 1:28 AM, Simon Peyton Jones <[email protected]> > wrote: > > Absolutely. There’s a whole module that does this: OptCoercion. If you > want to see what programs look like without coercion optimisation, try > –fno-opt-coercion. > > > > The rules are described in our paper *Evidence normalization in System > FC: http://research.microsoft.com/en-us/um/people/simonpj/papers/ext-f/ > <http://research.microsoft.com/en-us/um/people/simonpj/papers/ext-f/>* > > > > I hope that’s useful. > > > > Simon > > > > *From:* ghc-devs [mailto:[email protected]] *On Behalf Of *Conal > Elliott > *Sent:* 07 May 2014 04:50 > *To:* [email protected] > *Subject:* Simplifying casts and beta-reduction > > > > I'm looking for tools to help simplify Core terms that involve casts. In > particular, I want to beta-reduce when the function is wrapped with a cast. > Do the GHC sources have such utility functions? > > Here is an example of a lambda expression with a cast. In context, it's > applied to two type arguments and two dictionary arguments and returns a > function of one more argument. (The function `(-->)` is defined as `(f --> > h) g = h . g . f`.) > > > ((\ (@ a8) (@ b) > > ($dEncodable :: Encodable a8) > > ($dEncodable1 :: Encodable b) -> > > case $dEncodable of _ > > D:Encodable _ tpl_B3 -> > > case $dEncodable1 of _ > > D:Encodable tpl_B2 _ -> > > \ (g :: a8 -> b) (eta :: Encode a8) -> tpl_B2 (g (tpl_B3 > eta)) > > ) > > `cast` (forall a8 b. > > <Encodable a8>_R > > -> <Encodable b>_R > > -> <a8 -> b>_R > > -> Sub (Sym (TFCo:R:Encode(->)[0] <a8>_N <b>_N)) > > :: (forall a8 b. (Encodable a8, Encodable b) => > > (a8 -> b) -> Encode a8 -> Encode b) > > ~# > > (forall a8 b. (Encodable a8, Encodable b) => > > (a8 -> b) -> Encode (a8 -> b)))) > > I can imagine pushing the `cast` down through the type lambdas while > stripping off `forall` coercions, then pushing the remaining `cast` through > the dictionary arguments, while stripping off the outer `<Encodable t>_R > ->` coercion wrappers, and then pushing the cast into the `case` > alternatives and the lambda body, leaving something like > > > (\ (@ a8) (@ b) > > ($dEncodable :: Encodable a8) > > ($dEncodable1 :: Encodable b) -> > > case $dEncodable of _ > > D:Encodable _ tpl_B3 -> > > case $dEncodable1 of _ > > D:Encodable tpl_B2 _ -> > > \ (g :: a8 -> b) -> > > (\ (eta :: Encode a8) -> tpl_B2 (g (tpl_B3 eta))) > > `cast` (Sub (Sym (TFCo:R:Encode(->)[0] <a8>_N <b>_N)) > > :: (Encode a8 -> Encode b) > > ~# > > (Encode (a8 -> b)))) > > Now, given type, dictionary, and function arguments, I think we could > beta-reduce. > > Before I try implementing these transformations, does something like them > already exist in GHC? > > Thanks, -- Conal > > > > >
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