content: {-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, FlexibleContexts, TypeFamilies #-}
  module PushedInAsGivens where
  
  
  type family F a
  
  
  
  bar y = let foo :: (F Int ~ [a]) => a -> Int
              foo x = length [x,y]
          in (y,foo y)
  
  
  -- This example demonstrates why we need to push in
  -- an unsolved wanted as a given and not a given/solved.
  -- [Wanted] F Int ~ [beta]
  --- forall a. F Int ~ [a] => a ~ beta
  -- We push in the [Wanted] as given, it will interact and solve the implication
  -- constraint, and finally we quantify over F Int ~ [beta]. If we push it in as
  -- Given/Solved, it will be discarded when we meet the given (F Int ~ [a]) and
  -- we will not be able to solve the implication constraint.
  
  -- Oct 14: actually this example is _really_ strange, and doesn't illustrate
  -- the real issue in #4935, for which there is a separate test
  --
  -- The example here requires us to infer a type
  --   bar :: F Int ~ [a] => ...
  -- which is a strange type to quantify over; better to complain about
  -- having no instance for F Int.
  
  
  