Control.Monad.Trans.Ether.Dispatch

Type-level machinery to manipulate constraints on the monad transformer stack.

Out of the box it provides the following dispatch strategies:

• tagAttach to use functions defined using untagged monad classes as if they were defined using tagged ones.
• tagReplace to use functions defined using one tag as if they were defined using another one.

import qualified Control.Monad.State as T
import Control.Ether.TH (ethereal)
import Control.Monad.Ether.State (MonadState)
import Control.Monad.Trans.Ether.Dispatch (tagAttach, tagDispatch)

ethereal "Foo" "foo"
ethereal "Bar" "bar"

f :: T.MonadState Int m => m String
f = fmap show T.get

g :: MonadState Foo Int m => m String
g = tagAttach foo f

h :: MonadState Bar Int m => m String
h = tagReplace foo bar g

The DispatchT monad transformer

data DispatchT dp m a

Wrap a monad to change its tags. Under the hood this is simply IdentityT, all the work is happening on the type level.

Instances

MonadBase b m => MonadBase b (DispatchT k dp m)

MonadBaseControl b m => MonadBaseControl b (DispatchT k dp m)

MFunctor (DispatchT k dp)

MMonad (DispatchT k dp)

MonadTrans (DispatchT k dp)

MonadTransControl (DispatchT k dp)

LiftLocal (DispatchT k dp)

LiftCallCC (DispatchT k dp)

LiftPass (DispatchT k dp)

LiftListen (DispatchT k dp)

LiftCatch (DispatchT k dp)

Monad m => Monad (DispatchT k dp m)

Functor m => Functor (DispatchT k dp m)

MonadFix m => MonadFix (DispatchT k dp m)

Applicative m => Applicative (DispatchT k dp m)

Alternative m => Alternative (DispatchT k dp m)

MonadPlus m => MonadPlus (DispatchT k dp m)

MonadThrow m => MonadThrow (DispatchT k dp m)

MonadCatch m => MonadCatch (DispatchT k dp m)

MonadMask m => MonadMask (DispatchT k dp m)

MonadIO m => MonadIO (DispatchT k dp m)

Generic (DispatchT k dp m a)

type StT (DispatchT k dp) a = StT IdentityT a

type StT (DispatchT k dp) a = StT (DispatchT k dp) a

type StM (DispatchT k dp m) a = ComposeSt (DispatchT k dp) m a

type Rep (DispatchT k dp m a)

Dispatch types and functions

data K_TagAttach t

Encode type-level information for tagAttach.

Constructors

TagAttach t

data K_TagReplace tOld tNew

Encode type-level information for tagReplace.

Constructors

TagReplace tOld tNew

tagAttach :: proxy t -> DispatchTagAttachT t m a -> m a

Attach a tag to untagged transformers.

tagReplace :: proxy tOld -> proxy tNew -> DispatchTagReplaceT tOld tNew m a -> m a

Replace a tag with another tag.