-- Recovery of types, opaque types
-- This scenario demands propagation of types up in the tree of terms

:set -XExistentialQuantification -XDeriveDataTypeable -XGeneralizedNewtypeDeriving
:l Test 
let t = O (map Just [[1 :: Int,1],[2,2]])
:p t
seq _t1 ()  -- The contents of the opaque
:p t
seq _t3 ()  -- The tail of the list
:p t
seq _t5 ()  -- The 2nd element of the list
:p t
seq _t7 () -- The 1st element of the outer list

:p t       
 -- The 1st Just must be completely typed, as we know the type of the list