GHC HEAD trouble

[ggreif]

I get below errors when building with HEAD GHC

src/Indexed/Types.hs:142:10: error:
    Could not deduce (Typeable At)
      arising from the superclasses of an instance declaration
    from the context: (Data a, Typeable i, i ~ j)
      bound by the instance declaration at src/Indexed/Types.hs:142:10-55
    In the instance declaration for ?Data (At a i j)?

src/Indexed/Types.hs:193:10: error:
    Could not deduce (Typeable Coat)
      arising from the superclasses of an instance declaration
    from the context: (Data a, Typeable i, i ~ j)
      bound by the instance declaration at src/Indexed/Types.hs:193:10-57
    In the instance declaration for ?Data (Coat a i j)?

I did not analyse why this happens.

[michaelt]

This fails in ghc-7.10.1 too, but this simplifying declaration works:

 data At :: * -> k -> k -> * where  At :: a -> At a k k
   deriving Typeable
 deriving instance (Data a, Typeable (At a i j), i ~ j) => Data (At a i j)

I can't tell if the derived instance would be as useful, or if this is a sign of a bug in the Typeable machinery.

[ggreif]

This looks like a bug. It also pulls in

{-# LANGUAGE DeriveDataTypeable, FlexibleContexts, UndecidableInstances #-}

@michaelt to get it compiling I also had to change here:

@@ -21,7 +21,7 @@
 module Indexed.Types
   (
   -- * Natural Transformations
-    (~>)()
+    type (~>)()
   , (:~>)(Nat,($$))
   -- * Limits
   , Lim

did you see this too with 7.10.1 ?

[ggreif]

All the changes I have together so far:

diff --git a/src/Indexed/Types.hs b/src/Indexed/Types.hs
index 7af5513..bc7fb36 100644
--- a/src/Indexed/Types.hs
+++ b/src/Indexed/Types.hs
@@ -6,7 +6,7 @@
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE Trustworthy #-}
 {-# LANGUAGE ScopedTypeVariables #-}
-{-# LANGUAGE DeriveDataTypeable #-}
+{-# LANGUAGE DeriveDataTypeable, FlexibleContexts, UndecidableInstances #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Indexed.Types
@@ -21,7 +21,7 @@
 module Indexed.Types
   (
   -- * Natural Transformations
-    (~>)()
+    type (~>)
   , (:~>)(Nat,($$))
   -- * Limits
   , Lim
@@ -139,7 +139,7 @@ instance (Monoid m, i ~ j) => Monoid (At m i j) where
 -- | Type alias for indexed monads, functors, etc. in Bob Atkey's style.
 type Atkey f i j a = f (At a j) i

-instance (Data a, Typeable i, i ~ j) => Data (At a i j) where
+instance (Data a, Typeable (At a i j), i ~ j) => Data (At a i j) where
   gfoldl f z (At a) = z At `f` a
   toConstr _ = atConstr
   gunfold k z c = case constrIndex c of
@@ -190,7 +190,7 @@ uncoat (Coat a) = a
 -- | Type alias for indexed monads, functors, etc. in Bob Atkey's style.
 type Coatkey f i j a = f (Coat a j) i

-instance (Data a, Typeable i, i ~ j) => Data (Coat a i j) where
+instance (Data a, Typeable (Coat a i j), i ~ j) => Data (Coat a i j) where
   gfoldl f z (Coat a) = z (\x -> Coat x) `f` a
   toConstr _ = coatConstr
   gunfold k z c = case constrIndex c of

[michaelt]

That was with

{-# LANGUAGE FlexibleContexts #-} 
{-# LANGUAGE UndecidableInstances #-}

by the way. Elsewhere we run into trouble with Coat:

 imapCoat :: (IFunctor f) => (a -> b) -> f (Coat a i) ~> f (Coat b i)
 imapCoat f = imap $ \ c -> Coat $ case c of Coat a -> f a
 {-# INLINE imapCoat #-}

Like a number of similar definitions, this yields:

Couldn't match type ‘i’ with ‘x1’
  ‘i’ is a rigid type variable bound by
      the type signature for
        imapCoat :: IFunctor f => (a -> b) -> f (Coat a i) ~> f (Coat b i)
      at src/Indexed/Functor.hs:65:13
  ‘x1’ is a rigid type variable bound by
       a type expected by the context: Coat a i x1 -> Coat b i x1
       at src/Indexed/Functor.hs:66:14
Expected type: Coat b i x1
  Actual type: Coat b x1 x1
Relevant bindings include
  c :: Coat a i x1 (bound at src/Indexed/Functor.hs:66:23)
  imapCoat :: (a -> b) -> f (Coat a i) ~> f (Coat b i)
    (bound at src/Indexed/Functor.hs:66:1)
In the expression: Coat $ case c of { Coat a -> f a }
In the second argument of ‘($)’, namely
  ‘\ c -> Coat $ case c of { Coat a -> f a }’
In the expression: imap $ \ c -> Coat $ case c of { Coat a -> f a }

[michaelt]

@ggreif Sorry, I missed those intervening messages, I think I had the text box open for the above. If you make the changes you mentioned, does the rest of the package compile with HEAD? As I said, it seems still to break when it gets to Index.Functor with ghc-7.10.1

[wavewave]

Hi! any update on this build issue on ghc 7.10?

[wavewave]

It looks like the diff by @ggreif works for me with ghc 7.10.2. (at least compilable, haven't tested it yet)

[wavewave]

Ah. I have this error now.

[16 of 16] Compiling Indexed.Comonad.Store ( src/Indexed/Comonad/Store.hs, dist/build/Indexed/Comonad/Store.o )

src/Indexed/Comonad/Store.hs:18:21:
    The second argument of ‘~>’ should have kind ‘u1 -> *’,
      but ‘s’ has kind ‘v1 -> *’
    In the type ‘w a ~> s’
    In the class declaration for ‘IComonadStore’