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T15290a.hs:25:12: error: [GHC-18872]
• Couldn't match representation of type: m (Int, IntStateT m a1)
with that of: m (Int, StateT Int m a1)
arising from a use of ‘coerce’
NB: We cannot know what roles the parameters to ‘m’ have;
we must assume that the role is nominal
• In the expression:
coerce
@(forall a. StateT Int m (StateT Int m a) -> StateT Int m a)
@(forall a. IntStateT m (IntStateT m a) -> IntStateT m a) join
In an equation for ‘join’:
join
= coerce
@(forall a. StateT Int m (StateT Int m a) -> StateT Int m a)
@(forall a. IntStateT m (IntStateT m a) -> IntStateT m a) join
In the instance declaration for ‘Monad (IntStateT m)’
• Relevant bindings include
join :: IntStateT m (IntStateT m a) -> IntStateT m a
(bound at T15290a.hs:25:5)
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