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  • Simon Peyton Jones's avatar
    Make the LiberateCase transformation understand associated types · 7aa3f524
    Simon Peyton Jones authored 
    Consider this FC program:
	data family AT a :: *
	data instance AT Int = T1 Int Int

	f :: AT Int -> Int
	f t = case t of DEFAULT -> <body>

We'd like to replace the DEFAULT by a use of T1, so that if 
we scrutinise t inside <body> we share the evaluation:

	f t = case (t `cast` co) of T1 x y -> <body>

I decided to do this as part of the liberate-case transformation,
which is already trying to avoid redundant evals.  

The new transformation requires knowledge of the family instance
environment, so I had to extend ModGuts to carry the fam_inst_env,
and put that envt into the liberate-case environment. 

Otherwise it's all pretty straightforward.
    7aa3f524