[Haskell-beginners] Is it possible to "run" JSON Parser?

[Baa]

Hello List again! :)

If I have a `FromJSON` instance, with `parseJSON` which translates
`Value` to MyType, how can I run this parser like I "run"
state/writer/reader monads? I mean not decoding of a bytestring
representation:

  decode::ByteString -> Maybe MyType

but

  run::Value -> Maybe MyType

The reason is that I have already collected Value's , and I have
parsers, so what is the problem, it would seem, to run parser on the
Value - to convert `Value` into `Maybe MyType`... Is it possible?

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Best regards, Paul