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 | Haskell98 |
Control.Monad.Trans.Accum
Description
The lazy
AccumT
monad transformer, which adds accumulation
capabilities (such as declarations or document patches) to a given monad.
This monad transformer provides append-only accumulation during the computation. For more general access, 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
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.
The
return
function produces the output
mempty
, while
>>=
combines the outputs of the subcomputations using
mappend
.
This monad transformer is similar to both state and writer monad transformers. Thus it can be seen as
- a restricted append-only version of a state monad transformer or
- a writer monad transformer with the extra ability to read all previous output.
Constructors
AccumT (w -> m (a, w)) |
Instances
Monoid w => MonadTrans ( AccumT w) Source # | |
( Monoid w, Functor m, Monad m) => Monad ( AccumT w m) Source # | |
Functor m => Functor ( AccumT w m) Source # | |
( Monoid w, Functor m, MonadFix m) => MonadFix ( AccumT w m) Source # | |
( Monoid w, MonadFail m) => MonadFail ( AccumT w m) Source # | |
( Monoid w, Functor m, Monad m) => Applicative ( AccumT w m) Source # | |
Defined in Control.Monad.Trans.Accum Methods pure :: a -> AccumT w m a Source # (<*>) :: AccumT w m (a -> b) -> AccumT w m a -> AccumT w m b Source # liftA2 :: (a -> b -> c) -> AccumT w m a -> AccumT w m b -> AccumT w m c Source # (*>) :: AccumT w m a -> AccumT w m b -> AccumT w m b Source # (<*) :: AccumT w m a -> AccumT w m b -> AccumT w m a Source # |
|
( Monoid w, Functor m, MonadIO m) => MonadIO ( AccumT w m) Source # | |
( Monoid w, Functor m, MonadPlus m) => Alternative ( AccumT w m) Source # | |
( Monoid w, Functor m, MonadPlus m) => MonadPlus ( AccumT w m) Source # | |
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.