Thanks Ömer! I'm able to get dictionaries for the superclasses of a class now, but I get an error whenever I try to get a dictionary for a super-superclass. Here's the Haskell expression I'm working with: test1 :: Floating a => a -> a test1 x1 = x1+x1 The original core is: + @ a $dNum_aJu x1 x1 But my plugin is replacing it with the core: + @ a ($p1Fractional ($p1Floating $dFloating_aJq)) x1 x1 The only difference is the way I'm getting the Num dictionary. The corresponding AST (annotated with variable names and types) is: App (App (App (App (Var +::forall a. Num a => a -> a -> a) (Type a) ) (App (Var $p1Fractional::forall a. Fractional a => Num a) (App (Var $p1Floating::forall a. Floating a => Fractional a) (Var $dFloating_aJq::Floating a) ) ) ) (Var x1::'a') ) (Var x1::'a') When I insert, GHC gives the following error: ghc: panic! (the 'impossible' happened) (GHC version 7.10.1 for x86_64-unknown-linux): expectJust cpeBody:collect_args What am I doing wrong with extracting these super-superclass dictionaries? I've looked up the code for cpeBody in GHC, but I can't figure out what it's trying to do, so I'm not sure why it's failing on my core. On Mon, Aug 24, 2015 at 7:10 PM, Ömer Sinan Ağacan <omeragacan@gmail.com> wrote:
Mike, here's a piece of code that may be helpful to you:
https://github.com/osa1/sc-plugin/blob/master/src/Supercompilation/Show.hs
Copy this module to your plugin, it doesn't have any dependencies other than ghc itself. When your plugin is initialized, update `dynFlags_ref` with your DynFlags as first thing to do. Then use Show instance to print AST directly.
Horrible hack, but very useful for learning purposes. In fact, I don't know how else we can learn what Core is generated for a given code, and reverse-engineer to figure out details.
Hope it helps.
2015-08-24 21:59 GMT-04:00 Ömer Sinan Ağacan <omeragacan@gmail.com>:
Lets say I'm running the plugin on a function with signature `Floating a => a -> a`, then the plugin has access to the `Floating` dictionary for the type. But if I want to add two numbers together, I need the `Num` dictionary. I know I should have access to `Num` since it's a superclass of `Floating`. How can I get access to these superclass dictionaries?
I don't have a working code for this but this should get you started:
let ord_dictionary :: Id = ... ord_class :: Class = ... in mkApps (Var (head (classSCSels ord_class))) [Var ord_dictionary]
I don't know how to get Class for Ord. I do `head` here because in the case of Ord we only have one superclass so `classSCSels` should have one Id. Then I apply ord_dictionary to this selector and it should return dictionary for Eq.
I assumed you already have ord_dictionary, it should be passed to your function already if you had `(Ord a) => ` in your function.
Now I realized you asked for getting Num from Floating. I think you should follow a similar path except you need two applications, first to get Fractional from Floating and second to get Num from Fractional:
mkApps (Var (head (classSCSels fractional_class))) [mkApps (Var (head (classSCSels floating_class))) [Var floating_dictionary]]
Return value should be a Num dictionary.