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T9222.hs:13:3: error:
• Couldn't match type ‘b0’ with ‘b’
‘b0’ is untouchable
inside the constraints: a ~ '(b0, c0)
bound by the type of the constructor ‘Want’:
(a ~ '(b0, c0)) => Proxy b0
at T9222.hs:13:3
‘b’ is a rigid type variable bound by
the type of the constructor ‘Want’:
forall i j (a :: (i, j)) (b :: i) (c :: j).
((a ~ '(b, c)) => Proxy b) -> Want a
at T9222.hs:13:3
Expected type: Proxy b0
Actual type: Proxy b
• In the ambiguity check for ‘Want’
To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
In the definition of data constructor ‘Want’
In the data type declaration for ‘Want’
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