FreeNum experiments with recursion-schemes and free-functors

error.txt

/Users/dstoyano/work/app10/src/FreeNum.hs:17:1: error:
    • Could not deduce: Data.Constraint.Class1.Subset
                          (Data.Constraint.Class1.SuperClasses ExprClass)
                          (Data.Constraint.Class1.SuperClasses ExprClass)
        arising from a use of ‘Data.Constraint.Dict’
      from the context: Applicative f
        bound by the type signature for:
                   Data.Functor.Free.dictLifted :: forall (f :: * -> *) a.
                                                   Applicative f =>
                                                   Data.Constraint.Dict
                                                     (ExprClass
                                                        (Data.Functor.Free.LiftAFree ExprClass f a))
        at /Users/dstoyano/work/app10/src/FreeNum.hs:17:1-27
    • In the expression: Data.Constraint.Dict
      In an equation for ‘Data.Functor.Free.dictLifted’:
          Data.Functor.Free.dictLifted = Data.Constraint.Dict
      In the instance declaration for
        ‘Data.Functor.Free.ForallLifted ExprClass’
   |
17 | deriveInstances ''ExprClass
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^

/Users/dstoyano/work/app10/src/FreeNum.hs:17:1: error:
    • Could not deduce (Data.Constraint.Class1.HasSuperClasses
                          ExprClass)
        arising from a use of ‘Data.Constraint.Dict’
      from the context: Applicative f
        bound by the type signature for:
                   Data.Functor.Free.dictLifted :: forall (f :: * -> *) a.
                                                   Applicative f =>
                                                   Data.Constraint.Dict
                                                     (ExprClass
                                                        (Data.Functor.Free.LiftAFree ExprClass f a))
        at /Users/dstoyano/work/app10/src/FreeNum.hs:17:1-27
    • In the expression: Data.Constraint.Dict
      In an equation for ‘Data.Functor.Free.dictLifted’:
          Data.Functor.Free.dictLifted = Data.Constraint.Dict
      In the instance declaration for
        ‘Data.Functor.Free.ForallLifted ExprClass’
   |
17 | deriveInstances ''ExprClass
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^

/Users/dstoyano/work/app10/src/FreeNum.hs:32:24: error:
    • Could not deduce: Data.Constraint.Class1.Subset
                          (Data.Constraint.Class1.SuperClasses ExprClass)
                          (Data.Constraint.Class1.SuperClasses ExprClass)
        arising from a use of ‘constant’
    • In the expression: constant x
      In a case alternative: ConstantF x -> constant x
      In the second argument of ‘($)’, namely
        ‘\case
           AtomF a -> return a
           ConstantF x -> constant x
           ApplicationF a b -> app a b’
   |
32 |         ConstantF x -> constant x
   |                        ^^^^^^^^^^

/Users/dstoyano/work/app10/src/FreeNum.hs:32:24: error:
    • No instance for (Data.Constraint.Class1.HasSuperClasses
                         ExprClass)
        arising from a use of ‘constant’
    • In the expression: constant x
      In a case alternative: ConstantF x -> constant x
      In the second argument of ‘($)’, namely
        ‘\case
           AtomF a -> return a
           ConstantF x -> constant x
           ApplicationF a b -> app a b’
   |
32 |         ConstantF x -> constant x
   |                        ^^^^^^^^^^
Failed, no modules loaded.
Loaded GHCi configuration from /private/var/folders/s4/jhq2rgfd7z54466mw6xfzdm40000gn/T/ghci24303/ghci-script

FreeNum.hs

{-# LANGUAGE TemplateHaskell, TypeFamilies, DeriveFunctor, DeriveFoldable, DeriveTraversable, FlexibleInstances #-}
{-# LANGUAGE LambdaCase, FlexibleContexts, UndecidableInstances #-}

module FreeNum where

import Data.Functor.Free
import Data.Functor.Foldable
import Data.Functor.Foldable.TH

class ExprClass a where
        constant :: Int -> a
        app :: a -> [a] -> a

foo :: Free ExprClass String
foo = return "5"

deriveInstances ''ExprClass -- here error

data Expression a
        =   Application (Expression a) [Expression a]
        |   Atom a
        |   Constant Int
        deriving (Show, Eq, Functor)

makeBaseFunctor ''Expression

fromExpression :: Expression a -> Free ExprClass a
fromExpression = cata $ \case
        AtomF a -> return a
        ConstantF x -> constant x
        ApplicationF a b -> app a b


instance ExprClass (Expression a) where
     constant = Constant
     app = Application

toExpression :: Free ExprClass a -> Expression a
toExpression = rightAdjunct Atom

stack.yaml

resolver: nightly-2017-12-15

extra-deps:
  - base-4.9.1.0
  - syb-0.7
  - template-haskell-2.11.1.0
  - recursion-schemes-5.0.2
  - algebraic-classes-0.8
  - constraints-0.9
  - free-functors-0.8.1
  - free-4.12.4
  - comonad-5.0.2
  - cond-0.4.1.1
  - containers-0.5.8.2
  - data-partition-0.3.0.0

stack_version.txt

Version 1.6.1, Git revision f25811329bbc40b0c21053a8160c56f923e1201b (5435 commits) x86_64 hpack-0.20.0