T9222.stderr 798 Bytes
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T9222.hs:13:3: error:
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    • Couldn't match type ‘b0’ with ‘b’
        ‘b0’ is untouchable
          inside the constraints: a ~ '(b0, c0)
          bound by the type of the constructor ‘Want’:
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                     a ~ '(b0, c0) => Proxy b0
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          at T9222.hs:13:3
      ‘b’ is a rigid type variable bound by
        the type of the constructor ‘Want’:
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          forall i1 j1 (a :: (i1, j1)) (b :: i1) (c :: j1).
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          (a ~ '(b, c) => Proxy b) -> Want a
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        at T9222.hs:13:3
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      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’