[Haskell-cafe] Existential quantification of config data types

[Sumit Sahrawat, Maths & Computing, IIT (BHU)]

You can create a readLayer function that returns something like this:

   * data** OneLayer** =** forall** a. Layer a =>** OneLayer** a*

Such that we get:

*    -- Read next layer*
    *readLayer** :: Handle -> IO* *OneLayer*

Still, I feel that an ADT that combines all types is better as it fits the
problem perfectly. Every time you add a new layer it will generate warnings
for missing pattern matches.

Regards,
  Sumit
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