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T2664.hs:31:52:
Could not deduce (a ~ b)
from the context ((a :*: b) ~ Dual c, c ~ Dual (a :*: b))
bound by the type signature for
newPChan :: ((a :*: b) ~ Dual c, c ~ Dual (a :*: b)) =>
IO (PChan (a :*: b), PChan c)
at T2664.hs:23:5-12
‘a’ is a rigid type variable bound by
the instance declaration at T2664.hs:22:10
‘b’ is a rigid type variable bound by
the instance declaration at T2664.hs:22:10
Expected type: Dual (Dual a)
Actual type: b
Relevant bindings include
v :: MVar (Either (PChan a) (PChan b)) (bound at T2664.hs:24:9)
newPChan :: IO (PChan (a :*: b), PChan c) (bound at T2664.hs:23:5)
In the third argument of ‘pchoose’, namely ‘newPChan’
In the first argument of ‘E’, namely ‘(pchoose Right v newPChan)’
In the expression:
E (pchoose Right v newPChan) (pchoose Left v newPChan)
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