Class WriterT<W, M extends MonadRec<?,M>, A>

java.lang.Object

com.jnape.palatable.lambda.monad.transformer.builtin.WriterT<W,M,A>

Type Parameters:

W - the accumulation type

M - the monadic embedding

A - the result type

All Implemented Interfaces:

Applicative<A, WriterT<W,M,?>>, Functor<A, WriterT<W,M,?>>, Monad<A, WriterT<W,M,?>>, MonadBase<M, A, WriterT<W,?,?>>, MonadRec<A, WriterT<W,M,?>>, MonadWriter<W, A, WriterT<W,M,?>>, MonadT<M, A, WriterT<W,M,?>, WriterT<W,?,?>>

public final class WriterT<W, M extends MonadRec<?,M>, A>
extends Object
implements MonadWriter<W, A, WriterT<W,M,?>>, MonadT<M, A, WriterT<W,M,?>, WriterT<W,?,?>>

A monad transformer for Writer.

Field Summary

Fields

Modifier and Type	Field	Description
private final Pure<M>	pureM
private final Fn1<? super Monoid<W>, ? extends MonadRec<Tuple2<A,W>, M>>	writerFn

Constructor Summary

Constructors

Modifier	Constructor	Description
private	WriterT(Pure<M> pureM, Fn1<? super Monoid<W>, ? extends MonadRec<Tuple2<A,W>, M>> writerFn)

Method Summary

Modifier and Type	Method	Description
WriterT<W,M,A>	censor(Fn1<? super W, ? extends W> fn)	Update the accumulated state.
<B> WriterT<W,M,B>	discardL(Applicative<B, WriterT<W,M,?>> appB)	Sequence both this Applicative and appB, discarding this Applicative's result and returning appB.
<B> WriterT<W,M,A>	discardR(Applicative<B, WriterT<W,M,?>> appB)	Sequence both this Applicative and appB, discarding appB's result and returning this Applicative.
<MA extends MonadRec<A,M>> MA	evalWriterT(Monoid<W> monoid)	Given a Monoid for the accumulation, run the computation represented by this WriterT inside the monadic effect, ignoring the resulting accumulation, yielding the value in isolation.
<MW extends MonadRec<W,M>> MW	execWriterT(Monoid<W> monoid)	Given a Monoid for the accumulation, run the computation represented by this WriterT inside the monadic effect, ignoring the value, yielding the accumulation in isolation.
<B> WriterT<W,M,B>	flatMap(Fn1<? super A, ? extends Monad<B, WriterT<W,M,?>>> f)	Chain dependent computations that may continue or short-circuit based on previous results.
<B> WriterT<W,M,B>	fmap(Fn1<? super A, ? extends B> fn)	Covariantly transmute this functor's parameter using the given mapping function.
<B> Lazy<WriterT<W,M,B>>	lazyZip(Lazy<? extends Applicative<Fn1<? super A, ? extends B>, WriterT<W,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>> WriterT<W,N,B>	lift(MonadRec<B,N> mb)	Lift a new argument MonadRec into this MonadBase.
static <W> Lift<WriterT<W,?,?>>	liftWriterT()	Lift for WriterT.
static <W, M extends MonadRec<?,M>, A> WriterT<W,M,A>	listen(MonadRec<A,M> ma)	Lift a value embedded in a Monad into a WriterT.
<B> WriterT<W, M, Tuple2<A,B>>	listens(Fn1<? super W, ? extends B> fn)	Map the accumulation into a value and pair it with the current output.
<B> WriterT<W,M,B>	pure(B b)	Lift the value b into this applicative functor.
static <W, M extends MonadRec<?,M>> Pure<WriterT<W,M,?>>	pureWriterT(Pure<M> pureM)	The canonical Pure instance for WriterT.
<MAW extends MonadRec<Tuple2<A,W>, M>> MAW	runWriterT(Monoid<W> monoid)	Given a Monoid for the accumulation, run the computation represented by this WriterT inside the monadic effect, accumulate the written output in terms of the Monoid, and produce the accumulation and the result inside the Monad.
static <W, M extends MonadRec<?,M>> WriterT<W,M,Unit>	tell(MonadRec<W,M> mw)	Lift an accumulation embedded in a Monad into a WriterT.
<B> WriterT<W,M,B>	trampolineM(Fn1<? super A, ? extends MonadRec<RecursiveResult<A,B>, WriterT<W,M,?>>> fn)	Given some operation yielding a RecursiveResult inside this MonadRec, internally trampoline the operation until it yields a termination instruction.
static <W, M extends MonadRec<?,M>, A> WriterT<W,M,A>	writerT(MonadRec<Tuple2<A,W>, M> maw)	Lift a value and an accumulation embedded in a Monad into a WriterT.
<B> WriterT<W,M,B>	zip(Applicative<Fn1<? super A, ? extends B>, WriterT<W,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

pureM

private final Pure<M extends MonadRec<?,M>> pureM

writerFn

private final Fn1<? super Monoid<W>, ? extends MonadRec<Tuple2<A,W>, M extends MonadRec<?,M>>> writerFn

Constructor Details

WriterT

private WriterT(Pure<M> pureM,
 Fn1<? super Monoid<W>, ? extends MonadRec<Tuple2<A,W>, M>> writerFn)

Method Details

runWriterT

public <MAW extends MonadRec<Tuple2<A,W>, M>> MAW runWriterT(Monoid<W> monoid)

Given a Monoid for the accumulation, run the computation represented by this WriterT inside the monadic effect, accumulate the written output in terms of the Monoid, and produce the accumulation and the result inside the Monad.

Type Parameters:

MAW - the inferred MonadRec result

Parameters:

monoid - the accumulation Monoid

Returns:

the accumulation with the result

evalWriterT

public <MA extends MonadRec<A,M>> MA evalWriterT(Monoid<W> monoid)

Given a Monoid for the accumulation, run the computation represented by this WriterT inside the monadic effect, ignoring the resulting accumulation, yielding the value in isolation.

Type Parameters:

MA - the inferred MonadRec result

Parameters:

monoid - the accumulation Monoid

Returns:

the result

execWriterT

public <MW extends MonadRec<W,M>> MW execWriterT(Monoid<W> monoid)

Given a Monoid for the accumulation, run the computation represented by this WriterT inside the monadic effect, ignoring the value, yielding the accumulation in isolation.

Type Parameters:

MW - the inferred MonadRec accumulation

Parameters:

monoid - the accumulation Monoid

Returns:

the accumulation

listens

public <B> WriterT<W, M, Tuple2<A,B>> listens(Fn1<? super W, ? extends B> fn)

Map the accumulation into a value and pair it with the current output.

Specified by:

listens in interface MonadWriter<W, M extends MonadRec<?,M>, A>

Type Parameters:

B - the mapped output

Parameters:

fn - the mapping function

Returns:

the updated MonadWriter

censor

public WriterT<W,M,A> censor(Fn1<? super W, ? extends W> fn)

Update the accumulated state.

Specified by:

censor in interface MonadWriter<W, M extends MonadRec<?,M>, A>

Parameters:

fn - the update function

Returns:

the updated MonadWriter

lift

public <B, N extends MonadRec<?,N>> WriterT<W,N,B> lift(MonadRec<B,N> mb)

Lift a new argument MonadRec into this MonadBase.

Specified by:

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

Specified by:

lift in interface MonadT<M extends MonadRec<?,M>, A, WriterT<W, M extends MonadRec<?,M>, ?>, WriterT<W,?,?>>

Type Parameters:

B - the MonadRec carrier type

N - the argument MonadRec witness

Parameters:

mb - the argument MonadRec

Returns:

the new MonadBase

trampolineM

public <B> WriterT<W,M,B> trampolineM(Fn1<? super A, ? extends MonadRec<RecursiveResult<A,B>, WriterT<W,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<W, 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

fmap

public <B> WriterT<W,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<W, M extends MonadRec<?,M>>

Specified by:

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

Specified by:

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

Specified by:

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

Specified by:

fmap in interface MonadT<M extends MonadRec<?,M>, A, WriterT<W, M extends MonadRec<?,M>, ?>, WriterT<W,?,?>>

Specified by:

fmap in interface MonadWriter<W, 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)

pure

public <B> WriterT<W,M,B> pure(B b)

Lift the value b into this applicative functor.

Specified by:

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

Specified by:

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

Specified by:

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

Specified by:

pure in interface MonadT<M extends MonadRec<?,M>, A, WriterT<W, M extends MonadRec<?,M>, ?>, WriterT<W,?,?>>

Specified by:

pure in interface MonadWriter<W, 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

flatMap

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

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

Specified by:

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

Specified by:

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

Specified by:

flatMap in interface MonadT<M extends MonadRec<?,M>, A, WriterT<W, M extends MonadRec<?,M>, ?>, WriterT<W,?,?>>

Specified by:

flatMap in interface MonadWriter<W, M extends MonadRec<?,M>, A>

Type Parameters:

B - the resulting monad parameter type

Parameters:

f - the dependent computation over A

Returns:

the new monad instance

zip

public <B> WriterT<W,M,B> zip(Applicative<Fn1<? super A, ? extends B>, WriterT<W,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<W, M extends MonadRec<?,M>>

Specified by:

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

Specified by:

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

Specified by:

zip in interface MonadT<M extends MonadRec<?,M>, A, WriterT<W, M extends MonadRec<?,M>, ?>, WriterT<W,?,?>>

Specified by:

zip in interface MonadWriter<W, M extends MonadRec<?,M>, A>

Type Parameters:

B - the resulting applicative parameter type

Parameters:

appFn - the other applicative instance

Returns:

the mapped applicative

lazyZip

public <B> Lazy<WriterT<W,M,B>> lazyZip(Lazy<? extends Applicative<Fn1<? super A, ? extends B>, WriterT<W,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<W, M extends MonadRec<?,M>>

Specified by:

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

Specified by:

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

Specified by:

lazyZip in interface MonadT<M extends MonadRec<?,M>, A, WriterT<W, M extends MonadRec<?,M>, ?>, WriterT<W,?,?>>

Specified by:

lazyZip in interface MonadWriter<W, 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:

• Maybe
• Either

discardL

public <B> WriterT<W,M,B> discardL(Applicative<B, WriterT<W,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<W, M extends MonadRec<?,M>>

Specified by:

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

Specified by:

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

Specified by:

discardL in interface MonadT<M extends MonadRec<?,M>, A, WriterT<W, M extends MonadRec<?,M>, ?>, WriterT<W,?,?>>

Specified by:

discardL in interface MonadWriter<W, M extends MonadRec<?,M>, A>

Type Parameters:

B - the type of the returned Applicative's parameter

Parameters:

appB - the other Applicative

Returns:

appB

discardR

public <B> WriterT<W,M,A> discardR(Applicative<B, WriterT<W,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<W, M extends MonadRec<?,M>>

Specified by:

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

Specified by:

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

Specified by:

discardR in interface MonadT<M extends MonadRec<?,M>, A, WriterT<W, M extends MonadRec<?,M>, ?>, WriterT<W,?,?>>

Specified by:

discardR in interface MonadWriter<W, M extends MonadRec<?,M>, A>

Type Parameters:

B - the type of appB's parameter

Parameters:

appB - the other Applicative

Returns:

this Applicative

tell

public static <W, M extends MonadRec<?,M>>
WriterT<W,M,Unit> tell(MonadRec<W,M> mw)

Lift an accumulation embedded in a Monad into a WriterT.

Type Parameters:

W - the accumulation type

M - the Monad type

Parameters:

mw - the accumulation inside a Monad

Returns:

the WriterT

listen

public static <W, M extends MonadRec<?,M>, A>
WriterT<W,M,A> listen(MonadRec<A,M> ma)

Lift a value embedded in a Monad into a WriterT.

Type Parameters:

W - the accumulation type

M - the Monad type

A - the value type

Parameters:

ma - the value inside a Monad

Returns:

the WriterT

writerT

public static <W, M extends MonadRec<?,M>, A>
WriterT<W,M,A> writerT(MonadRec<Tuple2<A,W>, M> maw)

Lift a value and an accumulation embedded in a Monad into a WriterT.

Type Parameters:

W - the accumulation type

M - the Monad type

A - the value type

Parameters:

maw - the value and accumulation inside a Monad

Returns:

the WriterT

pureWriterT

public static <W, M extends MonadRec<?,M>>
Pure<WriterT<W,M,?>> pureWriterT(Pure<M> pureM)

The canonical Pure instance for WriterT.

Type Parameters:

W - the accumulation type

M - the argument Monad witness

Parameters:

pureM - the argument Monad Pure

Returns:

the Pure instance

liftWriterT

public static <W> Lift<WriterT<W,?,?>> liftWriterT()

Lift for WriterT.

Type Parameters:

W - the accumulated type

Returns:

the Monad lifted into WriterT