T9222.stderr 749 Bytes
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T9222.hs:13:3: error:
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    • Couldn't match type ‘c0’ with ‘c’
        ‘c0’ is untouchable
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          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:13:3-43
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      ‘c’ is a rigid type variable bound by
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        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:13:3-43
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    • 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’