Interface MonadT<M extends MonadRec<?,M>,A,MT extends MonadT<M,?,MT,T>,T extends MonadT<?,?,?,T>>
- Type Parameters:
M
- the argumentmonad
A
- the carrier typeMT
- theMonad
witnessT
- theMonadT
witness
- All Superinterfaces:
Applicative<A,
,MT> Functor<A,
,MT> Monad<A,
,MT> MonadBase<M,
,A, T> MonadRec<A,
MT>
- All Known Implementing Classes:
EitherT
,IdentityT
,IterateT
,LazyT
,MaybeT
,ReaderT
,SafeT
,StateT
,WriterT
Monad
transformer, exposing the argument Monad
as a type parameter.
While any two functors
and any two applicatives
can be composed in general, the
same is not true in general of any two monads
. However, there exist monads
that do
compose, in general, with any other Monad
. When this is the case, the combination of these
monads
with any other Monad
can offer composed implementations of pure
and
flatMap
for free, simply by relying on the other monad's
implementation of
both, as well as their own privileged knowledge about how to merge the nested flatMap
call. This can be thought of as "gluing" together two monads
, allowing easier access to their values,
as well as, in some cases, providing universally correct constructions of the composed short-circuiting algorithms.
The term "monad transformer" describes this particular encoding of monadic composition, and tends to be
named in terms of Monad
for which privileged knowledge must be known in order to eliminate during
flatmapping
.
For more information, read more about monad transformers.
- See Also:
-
Method Summary
Modifier and TypeMethodDescriptiondiscardL
(Applicative<B, MT> appB) Sequence both thisApplicative
andappB
, discarding thisApplicative's
result and returningappB
.discardR
(Applicative<B, MT> appB) Sequence both thisApplicative
andappB
, discardingappB's
result and returning thisApplicative
.Chain dependent computations that may continue or short-circuit based on previous results.Covariantly transmute this functor's parameter using the given mapping function.Given alazy
instance of this applicative over a mapping function, "zip" the two instances together using whatever application semantics the current applicative supports.pure
(B b) Lift the valueb
into this applicative functor.zip
(Applicative<Fn1<? super A, ? extends B>, MT> appFn) Given another instance of this applicative over a mapping function, "zip" the two instances together using whatever application semantics the current applicative supports.Methods inherited from interface com.jnape.palatable.lambda.monad.MonadRec
trampolineM
-
Method Details
-
lift
-
flatMap
Chain dependent computations that may continue or short-circuit based on previous results. -
pure
Lift the valueb
into this applicative functor.- Specified by:
pure
in interfaceApplicative<M extends MonadRec<?,
M>, A> - Specified by:
pure
in interfaceMonad<M extends MonadRec<?,
M>, A> - Specified by:
pure
in interfaceMonadRec<M extends MonadRec<?,
M>, A> - Type Parameters:
B
- the type of the returned applicative's parameter- Parameters:
b
- the value- Returns:
- an instance of this applicative over b
-
fmap
Covariantly transmute this functor's parameter using the given mapping function. Generally this method is specialized to return an instance of the class implementing Functor.- Specified by:
fmap
in interfaceApplicative<M extends MonadRec<?,
M>, A> - Specified by:
fmap
in interfaceFunctor<M extends MonadRec<?,
M>, A> - Specified by:
fmap
in interfaceMonad<M extends MonadRec<?,
M>, A> - Specified by:
fmap
in interfaceMonadRec<M extends MonadRec<?,
M>, A> - Type Parameters:
B
- the new parameter type- Parameters:
fn
- the mapping function- Returns:
- a functor over B (the new parameter type)
-
zip
Given another instance of this applicative over a mapping function, "zip" the two instances together using whatever application semantics the current applicative supports.- Specified by:
zip
in interfaceApplicative<M extends MonadRec<?,
M>, A> - Specified by:
zip
in interfaceMonad<M extends MonadRec<?,
M>, A> - Specified by:
zip
in interfaceMonadRec<M extends MonadRec<?,
M>, A> - Type Parameters:
B
- the resulting applicative parameter type- Parameters:
appFn
- the other applicative instance- Returns:
- the mapped applicative
-
lazyZip
default <B> Lazy<? extends MonadT<M,B, lazyZipMT, T>> (Lazy<? extends Applicative<Fn1<? super A, ? extends B>, MT>> lazyAppFn) Given alazy
instance of this applicative over a mapping function, "zip" the two instances together using whatever application semantics the current applicative supports. This is useful for applicatives that support lazy evaluation and early termination.- Specified by:
lazyZip
in interfaceApplicative<M extends MonadRec<?,
M>, A> - Specified by:
lazyZip
in interfaceMonad<M extends MonadRec<?,
M>, A> - Specified by:
lazyZip
in interfaceMonadRec<M extends MonadRec<?,
M>, A> - Type Parameters:
B
- the resulting applicative parameter type- Parameters:
lazyAppFn
- the lazy other applicative instance- Returns:
- the mapped applicative
- See Also:
-
discardL
Sequence both thisApplicative
andappB
, discarding thisApplicative's
result and returningappB
. This is generally useful for sequentially performing side-effects.- Specified by:
discardL
in interfaceApplicative<M extends MonadRec<?,
M>, A> - Specified by:
discardL
in interfaceMonad<M extends MonadRec<?,
M>, A> - Specified by:
discardL
in interfaceMonadRec<M extends MonadRec<?,
M>, A> - Type Parameters:
B
- the type of the returned Applicative's parameter- Parameters:
appB
- the other Applicative- Returns:
- appB
-
discardR
Sequence both thisApplicative
andappB
, discardingappB's
result and returning thisApplicative
. This is generally useful for sequentially performing side-effects.- Specified by:
discardR
in interfaceApplicative<M extends MonadRec<?,
M>, A> - Specified by:
discardR
in interfaceMonad<M extends MonadRec<?,
M>, A> - Specified by:
discardR
in interfaceMonadRec<M extends MonadRec<?,
M>, A> - Type Parameters:
B
- the type of appB's parameter- Parameters:
appB
- the other Applicative- Returns:
- this Applicative
-