Class ReaderT<R, M extends MonadRec<?,M>, A>

java.lang.Object

com.jnape.palatable.lambda.monad.transformer.builtin.ReaderT<R,M,A>

Type Parameters:

R - the input type

M - the returned MonadRec

A - the embedded output type

All Implemented Interfaces:

Applicative<A, ReaderT<R,M,?>>, Cartesian<R, A, ReaderT<?,M,?>>, Contravariant<R, Profunctor<?, A, ReaderT<?,M,?>>>, Functor<A, ReaderT<R,M,?>>, Profunctor<R, A, ReaderT<?,M,?>>, Monad<A, ReaderT<R,M,?>>, MonadBase<M, A, ReaderT<R,?,?>>, MonadReader<R, A, ReaderT<R,M,?>>, MonadRec<A, ReaderT<R,M,?>>, MonadT<M, A, ReaderT<R,M,?>, ReaderT<R,?,?>>

public final class ReaderT<R, M extends MonadRec<?,M>, A>
extends Object
implements MonadReader<R, A, ReaderT<R,M,?>>, Cartesian<R, A, ReaderT<?,M,?>>, MonadT<M, A, ReaderT<R,M,?>, ReaderT<R,?,?>>

A monad transformer for any function from some type R to some monadic embedding MonadRec<A, M>.

Field Summary

Fields

Modifier and Type	Field	Description
private final Fn1<? super R, ? extends MonadRec<A,M>>	f

Constructor Summary

Constructors

Modifier	Constructor	Description
private	ReaderT(Fn1<? super R, ? extends MonadRec<A,M>> f)

Method Summary

Modifier and Type	Method	Description
<B> ReaderT<R,M,B>	and(ReaderT<A,M,B> amb)	Left-to-right composition between ReaderT instances running under the same effect and compatible between their inputs and outputs.
static <R, M extends MonadRec<?,M>> ReaderT<R,M,R>	ask(Pure<M> pureM)	Given a Pure ask will give you access to the input within the monadic embedding
ReaderT<R, M, Tuple2<R,A>>	carry()	Pair the covariantly-positioned carrier type with the contravariantly-positioned carrier type.
<C> ReaderT<Tuple2<C,R>, M, Tuple2<C,A>>	cartesian()	Pair some type C to this profunctor's carrier types.
<Q> ReaderT<Q,M,A>	contraMap(Fn1<? super Q, ? extends R> fn)	Contravariantly map A <- B.
<Q,B> ReaderT<Q,M,B>	diMap(Fn1<? super Q, ? extends R> lFn, Fn1<? super A, ? extends B> rFn)	Dually map contravariantly over the left parameter and covariantly over the right parameter.
<Q> ReaderT<Q,M,A>	diMapL(Fn1<? super Q, ? extends R> fn)	Contravariantly map over the left parameter.
<B> ReaderT<R,M,B>	diMapR(Fn1<? super A, ? extends B> fn)	Covariantly map over the right parameter.
<B> ReaderT<R,M,B>	discardL(Applicative<B, ReaderT<R,M,?>> appB)	Sequence both this Applicative and appB, discarding this Applicative's result and returning appB.
<B> ReaderT<R,M,A>	discardR(Applicative<B, ReaderT<R,M,?>> appB)	Sequence both this Applicative and appB, discarding appB's result and returning this Applicative.
<B> ReaderT<R,M,B>	flatMap(Fn1<? super A, ? extends Monad<B, ReaderT<R,M,?>>> f)	Chain dependent computations that may continue or short-circuit based on previous results.
<B> ReaderT<R,M,B>	fmap(Fn1<? super A, ? extends B> fn)	Covariantly transmute this functor's parameter using the given mapping function.
<B> Lazy<ReaderT<R,M,B>>	lazyZip(Lazy<? extends Applicative<Fn1<? super A, ? extends B>, ReaderT<R,M,?>>> lazyAppFn)	Given a lazy instance of this applicative over a mapping function, "zip" the two instances together using whatever application semantics the current applicative supports.
<B, N extends MonadRec<?,N>> ReaderT<R,N,B>	lift(MonadRec<B,N> mb)	Lift a new argument MonadRec into this MonadBase.
static <R> Lift<ReaderT<R,?,?>>	liftReaderT()	Lift for ReaderT.
ReaderT<R,M,A>	local(Fn1<? super R, ? extends R> fn)	Modify this MonadReader's environment after reading it but before running the effect.
<MA extends MonadRec<A,M>, N extends MonadRec<?,N>, B> ReaderT<R,N,B>	mapReaderT(Fn1<? super MA, ? extends MonadRec<B,N>> fn)	Map the current monadic embedding to a new one in a potentially different Monad.
<B> ReaderT<R,M,B>	pure(B b)	Lift the value b into this applicative functor.
static <R, M extends MonadRec<?,M>> Pure<ReaderT<R,M,?>>	pureReaderT(Pure<M> pureM)	The canonical Pure instance for ReaderT.
static <R, M extends MonadRec<?,M>, A> ReaderT<R,M,A>	readerT(Fn1<? super R, ? extends MonadRec<A,M>> fn)	Lift a function (R -> Monad<A, M>) into a ReaderT instance.
<MA extends MonadRec<A,M>> MA	runReaderT(R r)	Run the computation represented by this ReaderT.
<B> ReaderT<R,M,B>	trampolineM(Fn1<? super A, ? extends MonadRec<RecursiveResult<A,B>, ReaderT<R,M,?>>> fn)	Given some operation yielding a RecursiveResult inside this MonadRec, internally trampoline the operation until it yields a termination instruction.
<B> ReaderT<R,M,B>	zip(Applicative<Fn1<? super A, ? extends B>, ReaderT<R,M,?>> 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 class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface Functor

coerce

Field Details

f

private final Fn1<? super R, ? extends MonadRec<A, M extends MonadRec<?,M>>> f

Constructor Details

ReaderT

private ReaderT(Fn1<? super R, ? extends MonadRec<A,M>> f)

Method Details

runReaderT

public <MA extends MonadRec<A,M>> MA runReaderT(R r)

Run the computation represented by this ReaderT.

Type Parameters:

MA - the witnessed target type

Parameters:

r - the input

Returns:

the embedded MonadRec

mapReaderT

public <MA extends MonadRec<A,M>, N extends MonadRec<?,N>, B>
ReaderT<R,N,B> mapReaderT(Fn1<? super MA, ? extends MonadRec<B,N>> fn)

Map the current monadic embedding to a new one in a potentially different Monad.

Type Parameters:

MA - the currently embedded Monad

N - the new Monad witness

B - the new carrier type

Parameters:

fn - the function

Returns:

the mapped ReaderT

and

public <B> ReaderT<R,M,B> and(ReaderT<A,M,B> amb)

Left-to-right composition between ReaderT instances running under the same effect and compatible between their inputs and outputs.

Type Parameters:

B - the final output type

Parameters:

amb - the next ReaderT to run

Returns:

the composed ReaderT

local

public ReaderT<R,M,A> local(Fn1<? super R, ? extends R> fn)

Modify this MonadReader's environment after reading it but before running the effect.

Specified by:

local in interface MonadReader<R, M extends MonadRec<?,M>, A>

Parameters:

fn - the modification function

Returns:

the MonadReader with a modified environment

lift

public <B, N extends MonadRec<?,N>> ReaderT<R,N,B> lift(MonadRec<B,N> mb)

Lift a new argument MonadRec into this MonadBase.

Specified by:

lift in interface MonadBase<R, M extends MonadRec<?,M>, A>

Specified by:

lift in interface MonadT<M extends MonadRec<?,M>, A, ReaderT<R, M extends MonadRec<?,M>, ?>, ReaderT<R,?,?>>

Type Parameters:

B - the MonadRec carrier type

N - the argument MonadRec witness

Parameters:

mb - the argument MonadRec

Returns:

the new MonadBase

flatMap

public <B> ReaderT<R,M,B> flatMap(Fn1<? super A, ? extends Monad<B, ReaderT<R,M,?>>> f)

Chain dependent computations that may continue or short-circuit based on previous results.

Specified by:

flatMap in interface Monad<R, M extends MonadRec<?,M>>

Specified by:

flatMap in interface MonadReader<R, M extends MonadRec<?,M>, A>

Specified by:

flatMap in interface MonadRec<R, M extends MonadRec<?,M>>

Specified by:

flatMap in interface MonadT<M extends MonadRec<?,M>, A, ReaderT<R, M extends MonadRec<?,M>, ?>, ReaderT<R,?,?>>

Type Parameters:

B - the resulting monad parameter type

Parameters:

f - the dependent computation over A

Returns:

the new monad instance

trampolineM

public <B> ReaderT<R,M,B> trampolineM(Fn1<? super A, ? extends MonadRec<RecursiveResult<A,B>, ReaderT<R,M,?>>> fn)

Given some operation yielding a RecursiveResult inside this MonadRec, internally trampoline the operation until it yields a termination instruction.

Stack-safety depends on implementations guaranteeing that the growth of the call stack is a constant factor independent of the number of invocations of the operation. For various examples of how this can be achieved in stereotypical circumstances, see the referenced types.

Specified by:

trampolineM in interface MonadRec<R, M extends MonadRec<?,M>>

Type Parameters:

B - the ultimate resulting carrier type

Parameters:

fn - the function to internally trampoline

Returns:

the trampolined MonadRec

See Also:

• for a basic implementation
• for a coproduct implementation
• for an implementation leveraging an already stack-safe Monad#flatMap(Fn1)
• for a monad transformer implementation

pure

public <B> ReaderT<R,M,B> pure(B b)

Lift the value b into this applicative functor.

Specified by:

pure in interface Applicative<R, M extends MonadRec<?,M>>

Specified by:

pure in interface Monad<R, M extends MonadRec<?,M>>

Specified by:

pure in interface MonadReader<R, M extends MonadRec<?,M>, A>

Specified by:

pure in interface MonadRec<R, M extends MonadRec<?,M>>

Specified by:

pure in interface MonadT<M extends MonadRec<?,M>, A, ReaderT<R, M extends MonadRec<?,M>, ?>, ReaderT<R,?,?>>

Type Parameters:

B - the type of the returned applicative's parameter

Parameters:

b - the value

Returns:

an instance of this applicative over b

fmap

public <B> ReaderT<R,M,B> fmap(Fn1<? super A, ? extends B> fn)

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 interface Applicative<R, M extends MonadRec<?,M>>

Specified by:

fmap in interface Functor<R, M extends MonadRec<?,M>>

Specified by:

fmap in interface Monad<R, M extends MonadRec<?,M>>

Specified by:

fmap in interface MonadReader<R, M extends MonadRec<?,M>, A>

Specified by:

fmap in interface MonadRec<R, M extends MonadRec<?,M>>

Specified by:

fmap in interface MonadT<M extends MonadRec<?,M>, A, ReaderT<R, M extends MonadRec<?,M>, ?>, ReaderT<R,?,?>>

Type Parameters:

B - the new parameter type

Parameters:

fn - the mapping function

Returns:

a functor over B (the new parameter type)

zip

public <B> ReaderT<R,M,B> zip(Applicative<Fn1<? super A, ? extends B>, ReaderT<R,M,?>> appFn)

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 interface Applicative<R, M extends MonadRec<?,M>>

Specified by:

zip in interface Monad<R, M extends MonadRec<?,M>>

Specified by:

zip in interface MonadReader<R, M extends MonadRec<?,M>, A>

Specified by:

zip in interface MonadRec<R, M extends MonadRec<?,M>>

Specified by:

zip in interface MonadT<M extends MonadRec<?,M>, A, ReaderT<R, M extends MonadRec<?,M>, ?>, ReaderT<R,?,?>>

Type Parameters:

B - the resulting applicative parameter type

Parameters:

appFn - the other applicative instance

Returns:

the mapped applicative

lazyZip

public <B> Lazy<ReaderT<R,M,B>> lazyZip(Lazy<? extends Applicative<Fn1<? super A, ? extends B>, ReaderT<R,M,?>>> lazyAppFn)

Given a lazy 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 interface Applicative<R, M extends MonadRec<?,M>>

Specified by:

lazyZip in interface Monad<R, M extends MonadRec<?,M>>

Specified by:

lazyZip in interface MonadReader<R, M extends MonadRec<?,M>, A>

Specified by:

lazyZip in interface MonadRec<R, M extends MonadRec<?,M>>

Specified by:

lazyZip in interface MonadT<M extends MonadRec<?,M>, A, ReaderT<R, M extends MonadRec<?,M>, ?>, ReaderT<R,?,?>>

Type Parameters:

B - the resulting applicative parameter type

Parameters:

lazyAppFn - the lazy other applicative instance

Returns:

the mapped applicative

See Also:

• Maybe
• Either

discardL

public <B> ReaderT<R,M,B> discardL(Applicative<B, ReaderT<R,M,?>> appB)

Sequence both this Applicative and appB, discarding this Applicative's result and returning appB. This is generally useful for sequentially performing side-effects.

Specified by:

discardL in interface Applicative<R, M extends MonadRec<?,M>>

Specified by:

discardL in interface Monad<R, M extends MonadRec<?,M>>

Specified by:

discardL in interface MonadReader<R, M extends MonadRec<?,M>, A>

Specified by:

discardL in interface MonadRec<R, M extends MonadRec<?,M>>

Specified by:

discardL in interface MonadT<M extends MonadRec<?,M>, A, ReaderT<R, M extends MonadRec<?,M>, ?>, ReaderT<R,?,?>>

Type Parameters:

B - the type of the returned Applicative's parameter

Parameters:

appB - the other Applicative

Returns:

appB

discardR

public <B> ReaderT<R,M,A> discardR(Applicative<B, ReaderT<R,M,?>> appB)

Sequence both this Applicative and appB, discarding appB's result and returning this Applicative. This is generally useful for sequentially performing side-effects.

Specified by:

discardR in interface Applicative<R, M extends MonadRec<?,M>>

Specified by:

discardR in interface Monad<R, M extends MonadRec<?,M>>

Specified by:

discardR in interface MonadReader<R, M extends MonadRec<?,M>, A>

Specified by:

discardR in interface MonadRec<R, M extends MonadRec<?,M>>

Specified by:

discardR in interface MonadT<M extends MonadRec<?,M>, A, ReaderT<R, M extends MonadRec<?,M>, ?>, ReaderT<R,?,?>>

Type Parameters:

B - the type of appB's parameter

Parameters:

appB - the other Applicative

Returns:

this Applicative

diMap

public <Q,B> ReaderT<Q,M,B> diMap(Fn1<? super Q, ? extends R> lFn,
 Fn1<? super A, ? extends B> rFn)

Dually map contravariantly over the left parameter and covariantly over the right parameter. This is isomorphic to diMapL(lFn).diMapR(rFn).

Specified by:

diMap in interface Cartesian<R, M extends MonadRec<?,M>, A>

Specified by:

diMap in interface Profunctor<R, M extends MonadRec<?,M>, A>

Type Parameters:

Q - the new left parameter type

B - the new right parameter type

Parameters:

lFn - the left parameter mapping function

rFn - the right parameter mapping function

Returns:

a profunctor over Z (the new left parameter type) and C (the new right parameter type)

diMapL

public <Q> ReaderT<Q,M,A> diMapL(Fn1<? super Q, ? extends R> fn)

Contravariantly map over the left parameter.

Specified by:

diMapL in interface Cartesian<R, M extends MonadRec<?,M>, A>

Specified by:

diMapL in interface Profunctor<R, M extends MonadRec<?,M>, A>

Type Parameters:

Q - the new left parameter type

Parameters:

fn - the mapping function

Returns:

a profunctor over Z (the new left parameter type) and C (the same right parameter type)

diMapR

public <B> ReaderT<R,M,B> diMapR(Fn1<? super A, ? extends B> fn)

Covariantly map over the right parameter. For all profunctors that are also functors, it should hold that diMapR(f) == fmap(f).

Specified by:

diMapR in interface Cartesian<R, M extends MonadRec<?,M>, A>

Specified by:

diMapR in interface Profunctor<R, M extends MonadRec<?,M>, A>

Type Parameters:

B - the new right parameter type

Parameters:

fn - the mapping function

Returns:

a profunctor over A (the same left parameter type) and C (the new right parameter type)

contraMap

public <Q> ReaderT<Q,M,A> contraMap(Fn1<? super Q, ? extends R> fn)

Contravariantly map A <- B.

Specified by:

contraMap in interface Cartesian<R, M extends MonadRec<?,M>, A>

Specified by:

contraMap in interface Contravariant<R, M extends MonadRec<?,M>>

Specified by:

contraMap in interface Profunctor<R, M extends MonadRec<?,M>, A>

Type Parameters:

Q - the new parameter type

Parameters:

fn - the mapping function

Returns:

the mapped Contravariant functor instance

cartesian

public <C> ReaderT<Tuple2<C,R>, M, Tuple2<C,A>> cartesian()

Pair some type C to this profunctor's carrier types.

Specified by:

cartesian in interface Cartesian<R, M extends MonadRec<?,M>, A>

Type Parameters:

C - the paired type

Returns:

the cartesian-strengthened profunctor

carry

public ReaderT<R, M, Tuple2<R,A>> carry()

Pair the covariantly-positioned carrier type with the contravariantly-positioned carrier type. This can be thought of as "carrying" or "inspecting" the left parameter.

Specified by:

carry in interface Cartesian<R, M extends MonadRec<?,M>, A>

Returns:

the profunctor with the first parameter carried

ask

public static <R, M extends MonadRec<?,M>>
ReaderT<R,M,R> ask(Pure<M> pureM)

Given a Pure ask will give you access to the input within the monadic embedding

Type Parameters:

R - the input and output type of the returned ReaderT

M - the returned Monad

Parameters:

pureM - the Pure instance for the given Monad

Returns:

the ReaderT

readerT

public static <R, M extends MonadRec<?,M>, A>
ReaderT<R,M,A> readerT(Fn1<? super R, ? extends MonadRec<A,M>> fn)

Lift a function (R -> Monad<A, M>) into a ReaderT instance.

Type Parameters:

R - the input type

M - the returned Monad

A - the embedded output type

Parameters:

fn - the function

Returns:

the ReaderT

pureReaderT

public static <R, M extends MonadRec<?,M>>
Pure<ReaderT<R,M,?>> pureReaderT(Pure<M> pureM)

The canonical Pure instance for ReaderT.

Type Parameters:

R - the input type

M - the argument Monad witness

Parameters:

pureM - the argument Monad Pure

Returns:

the Pure instance

liftReaderT

public static <R> Lift<ReaderT<R,?,?>> liftReaderT()

Lift for ReaderT.

Type Parameters:

R - the environment type

Returns:

the Monad lifted into ReaderT