Transaction Type Security

Question

I have a Transaction monad that looks like this:

newtype Transaction t m a = .. my monad stack here ..

t is the type of phantom that I use to make sure that the transactions I connect belong to the same file storage.

In my main loop iteration, a type type is used:

Transaction DB IO (Widget (Transaction DB IO ()))

The above type means: "a transaction that generates a user interface widget whose user inputs are converted to transactions for execution."

In addition, I have:

data Property m a = Property { get :: m a, set :: a -> m () }

which is extremely useful (especially because of its ability to link with FCLabels.

I make a lot of use Property (Transaction t m)to create my transactions.

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-, phantom, :

• Transaction ReadOnly Transaction ReadWrite . , , .

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Answer 1

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data Property rm wm a = Property { get :: rm a, set :: a -> wm () }

. :

newtype Transaction t c m a = .. my monad stack here

data Property mc c1 c2 a = Property { get :: mc c1 a, set :: a -> mc c2 () }

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newtype ReadOnly = ReadOnly

newtype ReadWrite = ReadWrite

class ReadContext rm where

class WriteContext rm where

instance ReadContext ReadOnly where
instance ReadContext ReadWrite where

instance WriteContext ReadWrite where

someGetter :: ReadContext c => Transaction t c m a

someSetter :: WriteContext c => a -> Transaction t c m ()

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