Class MaybeT<M extends MonadRec<?,M>, A>

java.lang.Object

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

Type Parameters:

M - the outer stack-safe monad

A - the carrier type

All Implemented Interfaces:

Applicative<A, MaybeT<M,?>>, Functor<A, MaybeT<M,?>>, Monad<A, MaybeT<M,?>>, MonadBase<M, A, MaybeT<?,?>>, MonadError<Unit, A, MaybeT<M,?>>, MonadRec<A, MaybeT<M,?>>, MonadT<M, A, MaybeT<M,?>, MaybeT<?,?>>

public final class MaybeT<M extends MonadRec<?,M>, A>
extends Object
implements MonadT<M, A, MaybeT<M,?>, MaybeT<?,?>>, MonadError<Unit, A, MaybeT<M,?>>

A monad transformer for Maybe.

Field Summary

Fields

Modifier and Type	Field	Description
private final MonadRec<Maybe<A>,M>	mma

Constructor Summary

Constructors

Modifier	Constructor	Description
private	MaybeT(MonadRec<Maybe<A>,M> mma)

Method Summary

Modifier and Type	Method	Description
MaybeT<M,A>	catchError(Fn1<? super Unit, ? extends Monad<A, MaybeT<M,?>>> recoveryFn)	Catch any thrown errors inside the Monad and resume normal operations.
<B> MaybeT<M,B>	discardL(Applicative<B, MaybeT<M,?>> appB)	Sequence both this Applicative and appB, discarding this Applicative's result and returning appB.
<B> MaybeT<M,A>	discardR(Applicative<B, MaybeT<M,?>> appB)	Sequence both this Applicative and appB, discarding appB's result and returning this Applicative.
boolean	equals(Object other)
MaybeT<M,A>	filter(Fn1<? super A, ? extends Boolean> predicate)	If the embedded value is present and satisfies predicate then return just the embedded value
<B> MaybeT<M,B>	flatMap(Fn1<? super A, ? extends Monad<B, MaybeT<M,?>>> f)	Chain dependent computations that may continue or short-circuit based on previous results.
<B> MaybeT<M,B>	fmap(Fn1<? super A, ? extends B> fn)	Covariantly transmute this functor's parameter using the given mapping function.
int	hashCode()
<B> Lazy<MaybeT<M,B>>	lazyZip(Lazy<? extends Applicative<Fn1<? super A, ? extends B>, MaybeT<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>> MaybeT<N,B>	lift(MonadRec<B,N> mb)	Lift a new argument MonadRec into this MonadBase.
static Lift<MaybeT<?,?>>	liftMaybeT()	Lift for MaybeT.
static <M extends MonadRec<?,M>, A> MaybeT<M,A>	maybeT(MonadRec<Maybe<A>,M> mma)	Static factory method for lifting a Monad<Maybe<A>, M> into a MaybeT.
MaybeT<M,A>	or(MaybeT<M,A> other)	Returns the first MaybeT that is an effect around just a result.
<B> MaybeT<M,B>	pure(B b)	Lift the value b into this applicative functor.
static <M extends MonadRec<?,M>> Pure<MaybeT<M,?>>	pureMaybeT(Pure<M> pureM)	The canonical Pure instance for MaybeT.
<MMA extends MonadRec<Maybe<A>,M>> MMA	runMaybeT()	Recover the full structure of the embedded Monad.
MaybeT<M,A>	throwError(Unit unit)	Throw an error value of type E into the monad.
String	toString()
<B> MaybeT<M,B>	trampolineM(Fn1<? super A, ? extends MonadRec<RecursiveResult<A,B>, MaybeT<M,?>>> fn)	Given some operation yielding a RecursiveResult inside this MonadRec, internally trampoline the operation until it yields a termination instruction.
<B> MaybeT<M,B>	zip(Applicative<Fn1<? super A, ? extends B>, MaybeT<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, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface Functor

coerce

Field Details

mma

private final MonadRec<Maybe<A>, M extends MonadRec<?,M>> mma

Constructor Details

MaybeT

private MaybeT(MonadRec<Maybe<A>,M> mma)

Method Details

runMaybeT

public <MMA extends MonadRec<Maybe<A>,M>> MMA runMaybeT()

Recover the full structure of the embedded Monad.

Type Parameters:

MMA - the witnessed target type

Returns:

the embedded Monad

filter

public MaybeT<M,A> filter(Fn1<? super A, ? extends Boolean> predicate)

If the embedded value is present and satisfies predicate then return just the embedded value

Parameters:

predicate - the predicate to apply to the embedded value

Returns:

maybe the satisfied value embedded under M

or

public MaybeT<M,A> or(MaybeT<M,A> other)

Returns the first MaybeT that is an effect around just a result.

Parameters:

other - the other MaybeT

Returns:

the first present MaybeT

throwError

public MaybeT<M,A> throwError(Unit unit)

Throw an error value of type E into the monad.

Specified by:

throwError in interface MonadError<Unit, A, MaybeT<M extends MonadRec<?,M>, ?>>

Parameters:

unit - the error type

Returns:

the monad

catchError

public MaybeT<M,A> catchError(Fn1<? super Unit, ? extends Monad<A, MaybeT<M,?>>> recoveryFn)

Catch any thrown errors inside the Monad and resume normal operations.

Specified by:

catchError in interface MonadError<Unit, A, MaybeT<M extends MonadRec<?,M>, ?>>

Parameters:

recoveryFn - the catch function

Returns:

the recovered Monad

lift

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

Lift a new argument MonadRec into this MonadBase.

Specified by:

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

Specified by:

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

Type Parameters:

B - the MonadRec carrier type

N - the argument MonadRec witness

Parameters:

mb - the argument MonadRec

Returns:

the new MonadBase

fmap

public <B> MaybeT<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<M extends MonadRec<?,M>, A>

Specified by:

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

Specified by:

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

Specified by:

fmap in interface MonadError<Unit, A, MaybeT<M extends MonadRec<?,M>, ?>>

Specified by:

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

Specified by:

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

Type Parameters:

B - the new parameter type

Parameters:

fn - the mapping function

Returns:

a functor over B (the new parameter type)

pure

public <B> MaybeT<M,B> pure(B b)

Lift the value b into this applicative functor.

Specified by:

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

Specified by:

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

Specified by:

pure in interface MonadError<Unit, A, MaybeT<M extends MonadRec<?,M>, ?>>

Specified by:

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

Specified by:

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

Type Parameters:

B - the type of the returned applicative's parameter

Parameters:

b - the value

Returns:

an instance of this applicative over b

zip

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

Specified by:

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

Specified by:

zip in interface MonadError<Unit, A, MaybeT<M extends MonadRec<?,M>, ?>>

Specified by:

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

Specified by:

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

Type Parameters:

B - the resulting applicative parameter type

Parameters:

appFn - the other applicative instance

Returns:

the mapped applicative

lazyZip

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

Specified by:

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

Specified by:

lazyZip in interface MonadError<Unit, A, MaybeT<M extends MonadRec<?,M>, ?>>

Specified by:

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

Specified by:

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

Type Parameters:

B - the resulting applicative parameter type

Parameters:

lazyAppFn - the lazy other applicative instance

Returns:

the mapped applicative

See Also:

• Maybe
• Either

flatMap

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

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

Specified by:

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

Specified by:

flatMap in interface MonadError<Unit, A, MaybeT<M extends MonadRec<?,M>, ?>>

Specified by:

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

Specified by:

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

Type Parameters:

B - the resulting monad parameter type

Parameters:

f - the dependent computation over A

Returns:

the new monad instance

trampolineM

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

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

discardL

public <B> MaybeT<M,B> discardL(Applicative<B, MaybeT<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<M extends MonadRec<?,M>, A>

Specified by:

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

Specified by:

discardL in interface MonadError<Unit, A, MaybeT<M extends MonadRec<?,M>, ?>>

Specified by:

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

Specified by:

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

Type Parameters:

B - the type of the returned Applicative's parameter

Parameters:

appB - the other Applicative

Returns:

appB

discardR

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

Specified by:

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

Specified by:

discardR in interface MonadError<Unit, A, MaybeT<M extends MonadRec<?,M>, ?>>

Specified by:

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

Specified by:

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

Type Parameters:

B - the type of appB's parameter

Parameters:

appB - the other Applicative

Returns:

this Applicative

equals

public boolean equals(Object other)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object

toString

public String toString()

Overrides:

toString in class Object

maybeT

public static <M extends MonadRec<?,M>, A>
MaybeT<M,A> maybeT(MonadRec<Maybe<A>,M> mma)

Static factory method for lifting a Monad<Maybe<A>, M> into a MaybeT.

Type Parameters:

M - the outer Monad unification parameter

A - the carrier type

Parameters:

mma - the Monad<Maybe<A>, M>

Returns:

the MaybeT

pureMaybeT

public static <M extends MonadRec<?,M>>
Pure<MaybeT<M,?>> pureMaybeT(Pure<M> pureM)

The canonical Pure instance for MaybeT.

Type Parameters:

M - the argument Monad witness

Parameters:

pureM - the argument Monad Pure

Returns:

the Pure instance

liftMaybeT

public static Lift<MaybeT<?,?>> liftMaybeT()

Lift for MaybeT. s

Returns:

the Monad lifted into MaybeT