[Haskell-cafe] Existential quantification of config data types

[Charlie Durham]

Hi,

I'm running into a weird problem i've never had before.

I want to define a datatype like:

data Network = forall a. Layer a => Network [a]

for which I have things that implement Layer, like

data TypicalLayer = ...

instance Layer TypicalLayer where ...

with this, I want to be able to load a Network from a config file where
Network can consist of different data types all implementing Layer.

Is there a nice way to do this without making a data type that combines all
of my layer types, something like:

data LayerType = TypicalLayerType TypicalLayer | AnotherLayerType
AnotherLayer ...

deriving (Show,Read)

Thanks for the help!

Charlie Durham
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