Copyright | (c) Nickolay Kudasov 2016 |
---|---|
License | BSD-style (see the file LICENSE) |
Maintainer | R.Paterson@city.ac.uk |
Stability | experimental |
Portability | portable |
Safe Haskell | Safe |
Language | Haskell2010 |
The lazy AccumT
monad transformer, which adds accumulation
capabilities (such as declarations or document patches) to a given monad.
Each computation has access to the combination of the input environment
and outputs added so far, and returns the outputs added.
In applications requiring only the ability to accumulate an output and to inspect the output so far, it would be considerably more efficient to use Control.Monad.Trans.State instead.
Synopsis
- type Accum w = AccumT w Identity
- accum :: Monad m => (w -> (a, w)) -> AccumT w m a
- runAccum :: Accum w a -> w -> (a, w)
- execAccum :: Accum w a -> w -> w
- evalAccum :: Monoid w => Accum w a -> w -> a
- mapAccum :: ((a, w) -> (b, w)) -> Accum w a -> Accum w b
- newtype AccumT w m a = AccumT (w -> m (a, w))
- runAccumT :: AccumT w m a -> w -> m (a, w)
- execAccumT :: Monad m => AccumT w m a -> w -> m w
- evalAccumT :: (Monad m, Monoid w) => AccumT w m a -> w -> m a
- mapAccumT :: (m (a, w) -> n (b, w)) -> AccumT w m a -> AccumT w n b
- look :: (Monoid w, Monad m) => AccumT w m w
- looks :: (Monoid w, Monad m) => (w -> a) -> AccumT w m a
- add :: Monad m => w -> AccumT w m ()
- liftCallCC :: CallCC m (a, w) (b, w) -> CallCC (AccumT w m) a b
- liftCallCC' :: CallCC m (a, w) (b, w) -> CallCC (AccumT w m) a b
- liftCatch :: Catch e m (a, w) -> Catch e (AccumT w m) a
- liftListen :: Monad m => Listen w m (a, s) -> Listen w (AccumT s m) a
- liftPass :: Monad m => Pass w m (a, s) -> Pass w (AccumT s m) a
- readerToAccumT :: (Functor m, Monoid w) => ReaderT w m a -> AccumT w m a
- writerToAccumT :: WriterT w m a -> AccumT w m a
- accumToStateT :: (Functor m, Monoid s) => AccumT s m a -> StateT s m a
The Accum monad
type Accum w = AccumT w Identity Source #
An accumulation monad parameterized by the type w
of output to accumulate.
This monad is a more complex extension of both the reader and writer
monads. The return
function produces the output mempty
, while m
uses the output of >>=
km
both to extend the initial environment
of k
and to combine with the output of k
:
In applications requiring only the ability to accumulate an output and to inspect the output so far, it would be considerably more efficient to use a state monad.
accum :: Monad m => (w -> (a, w)) -> AccumT w m a Source #
Construct an accumulation computation from a (result, output) pair.
(The inverse of runAccum
.)
runAccum :: Accum w a -> w -> (a, w) Source #
Unwrap an accumulation computation as a (result, output) pair.
(The inverse of accum
.)
The AccumT monad transformer
An accumulation monad parameterized by:
w
- the output to accumulate.m
- The inner monad.
This monad transformer is a more complex extension of both the reader
and writer monad transformers. The return
function produces the
output mempty
, while m
uses the output of >>=
km
both to
extend the initial environment of k
and to combine with the output
of k
:
In applications requiring only the ability to accumulate an output and to inspect the output so far, it would be considerably more efficient to use a state monad transformer.
AccumT (w -> m (a, w)) |
Instances
Monoid w => MonadTrans (AccumT w) Source # | |
(Monoid w, MonadFail m) => MonadFail (AccumT w m) Source # | |
Defined in Control.Monad.Trans.Accum | |
(Monoid w, Functor m, MonadFix m) => MonadFix (AccumT w m) Source # | |
Defined in Control.Monad.Trans.Accum | |
(Monoid w, Functor m, MonadIO m) => MonadIO (AccumT w m) Source # | |
Defined in Control.Monad.Trans.Accum | |
(Monoid w, Functor m, MonadPlus m) => Alternative (AccumT w m) Source # | |
(Monoid w, Functor m, Monad m) => Applicative (AccumT w m) Source # | |
Defined in Control.Monad.Trans.Accum | |
Functor m => Functor (AccumT w m) Source # | |
(Monoid w, Functor m, Monad m) => Monad (AccumT w m) Source # | |
(Monoid w, Functor m, MonadPlus m) => MonadPlus (AccumT w m) Source # | |
Generic (AccumT w m a) Source # | |
type Rep (AccumT w m a) Source # | |
Defined in Control.Monad.Trans.Accum |
runAccumT :: AccumT w m a -> w -> m (a, w) Source #
Unwrap an accumulation computation. For example, in the call
(value, locals) <- runAccumT action globals
the action is fed an initial environment globals
, and locals
is
the sum of all arguments to calls of add
executed by the action.
execAccumT :: Monad m => AccumT w m a -> w -> m w Source #
Extract the output from an accumulation computation.
execAccumT
m w =liftM
snd
(runAccumT
m w)
evalAccumT :: (Monad m, Monoid w) => AccumT w m a -> w -> m a Source #
Evaluate an accumulation computation with the given initial output history and return the final value, discarding the final output.
evalAccumT
m w =liftM
fst
(runAccumT
m w)
Accum operations
look :: (Monoid w, Monad m) => AccumT w m w Source #
is an action that fetches all the previously accumulated output.look
looks :: (Monoid w, Monad m) => (w -> a) -> AccumT w m a Source #
is an action that retrieves a function of the previously accumulated output.look
Lifting other operations
liftCallCC :: CallCC m (a, w) (b, w) -> CallCC (AccumT w m) a b Source #
Uniform lifting of a callCC
operation to the new monad.
This version rolls back to the original output history on entering the
continuation.
liftCallCC' :: CallCC m (a, w) (b, w) -> CallCC (AccumT w m) a b Source #
In-situ lifting of a callCC
operation to the new monad.
This version uses the current output history on entering the continuation.
It does not satisfy the uniformity property (see Control.Monad.Signatures).
liftCatch :: Catch e m (a, w) -> Catch e (AccumT w m) a Source #
Lift a catchE
operation to the new monad.
liftListen :: Monad m => Listen w m (a, s) -> Listen w (AccumT s m) a Source #
Lift a listen
operation to the new monad.
liftPass :: Monad m => Pass w m (a, s) -> Pass w (AccumT s m) a Source #
Lift a pass
operation to the new monad.
Monad transformations
readerToAccumT :: (Functor m, Monoid w) => ReaderT w m a -> AccumT w m a Source #
Convert a read-only computation into an accumulation computation.
writerToAccumT :: WriterT w m a -> AccumT w m a Source #
Convert a writer computation into an accumulation computation.