Package com.jnape.palatable.lambda.adt

Class Either<L,R>

java.lang.Object

com.jnape.palatable.lambda.adt.Either<L,R>

Type Parameters:

L - The left parameter type

R - The right parameter type

All Implemented Interfaces:

CoProduct2<L,R,Either<L,R>>, Applicative<R,Either<L,?>>, Bifunctor<L,R,Either<?,?>>, BoundedBifunctor<L,R,java.lang.Object,java.lang.Object,Either<?,?>>, Functor<R,Either<L,?>>, Monad<R,Either<L,?>>, MonadError<L,R,Either<L,?>>, MonadRec<R,Either<L,?>>, Traversable<R,Either<L,?>>

Direct Known Subclasses:

Either.Left, Either.Right

public abstract class Either<L,R>
extends java.lang.Object
implements CoProduct2<L,R,Either<L,R>>, MonadError<L,R,Either<L,?>>, MonadRec<R,Either<L,?>>, Traversable<R,Either<L,?>>, Bifunctor<L,R,Either<?,?>>

The binary tagged union, implemented as a specialized CoProduct2. General semantics tend to connote "success" values via the right value and "failure" values via the left values. Eithers are both Monads and Traversables over their right value and are Bifunctors over both values.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
private static class	Either.Left<L,R>
private static class	Either.Right<L,R>

Constructor Summary

Constructors

Modifier	Constructor	Description
private	Either()

Method Summary

Modifier and Type	Method	Description
<L2,R2> Either<L2,R2>	biMap(Fn1<? super L,? extends L2> leftFn, Fn1<? super R,? extends R2> rightFn)	Dually map covariantly over both the left and right parameters.
<L2> Either<L2,R>	biMapL(Fn1<? super L,? extends L2> fn)	Covariantly map over the left parameter.
<R2> Either<L,R2>	biMapR(Fn1<? super R,? extends R2> fn)	Covariantly map over the right parameter.
Either<L,R>	catchError(Fn1<? super L,? extends Monad<R,Either<L,?>>> recoveryFn)	Catch any thrown errors inside the Monad and resume normal operations.
<R2> Either<L,R2>	discardL(Applicative<R2,Either<L,?>> appB)	Sequence both this Applicative and appB, discarding this Applicative's result and returning appB.
<R2> Either<L,R>	discardR(Applicative<R2,Either<L,?>> appB)	Sequence both this Applicative and appB, discarding appB's result and returning this Applicative.
<C> Choice3<L,R,C>	diverge()	Diverge this coproduct by introducing another possible type that it could represent.
Either<L,R>	filter(Fn1<? super R,? extends java.lang.Boolean> pred, Fn0<L> leftFn0)	If this is a right value, apply pred to it.
Either<L,R>	filter(Fn1<? super R,? extends java.lang.Boolean> pred, Fn1<? super R,? extends L> leftFn)	If this is a right value, apply pred to it.
<R2> Either<L,R2>	flatMap(Fn1<? super R,? extends Monad<R2,Either<L,?>>> rightFn)	If a right value, unwrap it and apply it to rightFn, returning the resulting Either<L ,R>.
<R2> Either<L,R2>	fmap(Fn1<? super R,? extends R2> fn)	Covariantly transmute this functor's parameter using the given mapping function.
L	forfeit(Fn1<? super R,? extends L> forfeitFn)	Inverse of recover.
static <L,R> Either<L,R>	fromMaybe(Maybe<R> maybe, Fn0<L> leftFn0)	Convert a Maybe<R> into an Either<L, R>, supplying the left value from leftFn in the case of Maybe.nothing().
Either<R,L>	invert()	Swap the type parameters.
<R2> Lazy<Either<L,R2>>	lazyZip(Lazy<? extends Applicative<Fn1<? super R,? extends R2>,Either<L,?>>> 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.
static <L,R> Either<L,R>	left(L l)	Static factory method for creating a left value.
abstract <V> V	match(Fn1<? super L,? extends V> leftFn, Fn1<? super R,? extends V> rightFn)	Given two mapping functions (one from an L to a V, one from an R to a V), unwrap the value stored in this Either, apply the appropriate mapping function, and return the result.
Either<L,R>	merge(Fn2<? super L,? super L,? extends L> leftFn, Fn2<? super R,? super R,? extends R> rightFn, Either<L,R>... others)	Given two binary operators over L and R, merge multiple Either<L, R>s into a single Either<L, R>.
R	or(R defaultValue)	Return the value wrapped by this Either if it's a right value; otherwise, return defaultValue.
<T extends java.lang.Throwable> R	orThrow(Fn1<? super L,? extends T> throwableFn)	Return the wrapped value if this is a right; otherwise, map the wrapped left value to a T and throw it.
Either<L,R>	peek(Fn1<? super L,? extends IO<?>> leftEffect, Fn1<? super R,? extends IO<?>> rightEffect)	Deprecated. in favor of matching into an IO and explicitly running it
Either<L,R>	peek(Fn1<? super R,? extends IO<?>> effect)	Deprecated. in favor of matching into an IO and explicitly running it
<R2> Either<L,R2>	pure(R2 r2)	Lift the value b into this applicative functor.
static <L> Pure<Either<L,?>>	pureEither()	The canonical Pure instance for Either.
R	recover(Fn1<? super L,? extends R> recoveryFn)	"Recover" from a left value by applying a recoveryFn to the wrapped value and returning it in the case of a left value; otherwise, return the wrapped right value.
static <L,R> Either<L,R>	right(R r)	Static factory method for creating a right value.
Either<L,R>	throwError(L l)	Throw an error value of type E into the monad.
Maybe<R>	toMaybe()	In the left case, returns a Maybe.nothing(); otherwise, returns Maybe.maybe(A) around the right value.
<B> Either<L,B>	trampolineM(Fn1<? super R,? extends MonadRec<RecursiveResult<R,B>,Either<L,?>>> fn)	Given some operation yielding a RecursiveResult inside this MonadRec, internally trampoline the operation until it yields a termination instruction.
<R2,App extends Applicative<?,App>,TravB extends Traversable<R2,Either<L,?>>,AppTrav extends Applicative<TravB,App>> AppTrav	traverse(Fn1<? super R,? extends Applicative<R2,App>> fn, Fn1<? super TravB,? extends AppTrav> pure)	Apply fn to each element of this traversable from left to right, and collapse the results into a single resulting applicative, potentially with the assistance of the applicative's pure function.
static <R> Either<java.lang.Throwable,R>	trying(Fn0<? extends R> fn0)	Attempt to execute the Fn0, returning its result in a right value.
static <L,R> Either<L,R>	trying(Fn0<? extends R> fn0, Fn1<? super java.lang.Throwable,? extends L> leftFn)	Attempt to execute the Fn0, returning its result in a right value.
static Either<java.lang.Throwable,Unit>	trying(SideEffect sideEffect)	Attempt to execute the SideEffect, returning Unit in a right value.
static <L> Either<L,Unit>	trying(SideEffect sideEffect, Fn1<? super java.lang.Throwable,? extends L> leftFn)	Attempt to execute the SideEffect, returning Unit in a right value.
<R2> Either<L,R2>	zip(Applicative<Fn1<? super R,? extends R2>,Either<L,?>> 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 java.lang.Object

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

Methods inherited from interface com.jnape.palatable.lambda.adt.coproduct.CoProduct2

embed, project, projectA, projectB

Methods inherited from interface com.jnape.palatable.lambda.functor.Functor

coerce

Constructor Detail

Either

private Either()

Method Detail

or

public final R or(R defaultValue)

Return the value wrapped by this Either if it's a right value; otherwise, return defaultValue.

Parameters:

defaultValue - the value to return if this is a left

Returns:

the value wrapped by this Either if right; otherwise, defaultValue

recover

public final R recover(Fn1<? super L,? extends R> recoveryFn)

"Recover" from a left value by applying a recoveryFn to the wrapped value and returning it in the case of a left value; otherwise, return the wrapped right value.

Parameters:

recoveryFn - a function from L to R

Returns:

either the wrapped value (if right) or the result of the left value applied to recoveryFn

forfeit

public final L forfeit(Fn1<? super R,? extends L> forfeitFn)

Inverse of recover. If this is a right value, apply the wrapped value to forfeitFn and return it; otherwise, return the wrapped left value.

Parameters:

forfeitFn - a function from R to L

Returns:

either the wrapped value (if left) or the result of the right value applied to forfeitFn

orThrow

public final <T extends java.lang.Throwable> R orThrow(Fn1<? super L,? extends T> throwableFn)
                                                throws T extends java.lang.Throwable

Return the wrapped value if this is a right; otherwise, map the wrapped left value to a T and throw it.

Type Parameters:

T - the left parameter type (the throwable type)

Parameters:

throwableFn - a function from L to T

Returns:

the wrapped value if this is a right

Throws:

T - the result of applying the wrapped left value to throwableFn, if this is a left

T extends java.lang.Throwable

filter

public final Either<L,R> filter(Fn1<? super R,? extends java.lang.Boolean> pred,
                                      Fn0<L> leftFn0)

If this is a right value, apply pred to it. If the result is true, return the same value; otherwise, return the result of leftSupplier wrapped as a left value.

If this is a left value, return it.

Parameters:

pred - the predicate to apply to a right value

leftFn0 - the supplier of a left value if pred fails

Returns:

this if a left value or a right value that pred matches; otherwise, the result of leftSupplier wrapped in a left

filter

public final Either<L,R> filter(Fn1<? super R,? extends java.lang.Boolean> pred,
                                      Fn1<? super R,? extends L> leftFn)

If this is a right value, apply pred to it. If the result is true, return the same value; otherwise, return the results of applying the right value to leftFn wrapped as a left value.

Parameters:

pred - the predicate to apply to a right value

leftFn - the function from the right value to a left value if pred fails

Returns:

this is a left value or a right value that pred matches; otherwise, the result of leftFn applied to the right value, wrapped in a left

flatMap

public <R2> Either<L,R2> flatMap(Fn1<? super R,? extends Monad<R2,Either<L,?>>> rightFn)

If a right value, unwrap it and apply it to rightFn, returning the resulting Either<L ,R>. Otherwise, return the left value.

Note that because this monadic form of flatMap only supports mapping over a theoretical right value, the resulting Either must be invariant on the same left value to flatten properly.

Specified by:

flatMap in interface Monad<L,R>

Specified by:

flatMap in interface MonadError<L,R,Either<L,?>>

Specified by:

flatMap in interface MonadRec<L,R>

Type Parameters:

R2 - the new right parameter type

Parameters:

rightFn - the function to apply to a right value

Returns:

the Either resulting from applying rightFn to this right value, or this left value if left

trampolineM

public <B> Either<L,B> trampolineM(Fn1<? super R,? extends MonadRec<RecursiveResult<R,B>,Either<L,?>>> 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<L,R>

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 implementation, for an implementation leveraging an already stack-safe , for a implementation

invert

public final Either<R,L> invert()

Description copied from interface: CoProduct2

Swap the type parameters.

Specified by:

invert in interface CoProduct2<L,R,Either<L,R>>

Returns:

The inverted coproduct

merge

@SafeVarargs
public final Either<L,R> merge(Fn2<? super L,? super L,? extends L> leftFn,
                                     Fn2<? super R,? super R,? extends R> rightFn,
                                     Either<L,R>... others)

Given two binary operators over L and R, merge multiple Either<L, R>s into a single Either<L, R>. Note that merge biases towards left values; that is, if any left value exists, the result will be a left value, such that only unanimous right values result in an ultimate right value.

Parameters:

leftFn - the binary operator for L

rightFn - the binary operator for R

others - the other Eithers to merge into this one

Returns:

the merged Either

peek

@Deprecated
public Either<L,R> peek(Fn1<? super R,? extends IO<?>> effect)

Deprecated.

in favor of matching into an IO and explicitly running it

Perform side-effects against a wrapped right value, returning back the Either unaltered.

Parameters:

effect - the effecting consumer

Returns:

the Either, unaltered

peek

@Deprecated
public Either<L,R> peek(Fn1<? super L,? extends IO<?>> leftEffect,
                              Fn1<? super R,? extends IO<?>> rightEffect)

Deprecated.

in favor of matching into an IO and explicitly running it

Perform side-effects against a wrapped right or left value, returning back the Either unaltered.

Parameters:

leftEffect - the effecting consumer for left values

rightEffect - the effecting consumer for right values

Returns:

the Either, unaltered

match

public abstract <V> V match(Fn1<? super L,? extends V> leftFn,
                            Fn1<? super R,? extends V> rightFn)

Given two mapping functions (one from an L to a V, one from an R to a V), unwrap the value stored in this Either, apply the appropriate mapping function, and return the result.

Specified by:

match in interface CoProduct2<L,R,Either<L,R>>

Type Parameters:

V - the result type

Parameters:

leftFn - the left value mapping function

rightFn - the right value mapping function

Returns:

the result of applying the appropriate mapping function to the wrapped value

diverge

public <C> Choice3<L,R,C> diverge()

Diverge this coproduct by introducing another possible type that it could represent. As no morphisms can be provided mapping current types to the new type, this operation merely acts as a convenience method to allow the use of a more convergent coproduct with a more divergent one; that is, if a CoProduct3<String, Integer, Boolean> is expected, a CoProduct2<String, Integer> should suffice.

Generally, we use inheritance to make this a non-issue; however, with coproducts of differing magnitudes, we cannot guarantee variance compatibility in one direction conveniently at construction time, and in the other direction, at all. A CoProduct2 could not be a CoProduct3 without specifying all type parameters that are possible for a CoProduct3 - more specifically, the third possible type - which is not necessarily known at construction time, or even useful if never used in the context of a CoProduct3. The inverse inheritance relationship - CoProduct3 < CoProduct2 - is inherently unsound, as a CoProduct3 cannot correctly implement CoProduct2.match(com.jnape.palatable.lambda.functions.Fn1<? super A, ? extends R>, com.jnape.palatable.lambda.functions.Fn1<? super B, ? extends R>), given that the third type C is always possible.

For this reason, there is a diverge method supported between all CoProduct types of single magnitude difference.

Specified by:

diverge in interface CoProduct2<L,R,Either<L,R>>

Type Parameters:

C - the additional possible type of this coproduct

Returns:

a CoProduct3<A, B, C>

fmap

public final <R2> Either<L,R2> fmap(Fn1<? super R,? extends R2> 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<L,R>

Specified by:

fmap in interface Functor<L,R>

Specified by:

fmap in interface Monad<L,R>

Specified by:

fmap in interface MonadError<L,R,Either<L,?>>

Specified by:

fmap in interface MonadRec<L,R>

Specified by:

fmap in interface Traversable<L,R>

Type Parameters:

R2 - the new parameter type

Parameters:

fn - the mapping function

Returns:

a functor over B (the new parameter type)

biMapL

public final <L2> Either<L2,R> biMapL(Fn1<? super L,? extends L2> fn)

Covariantly map over the left parameter.

Specified by:

biMapL in interface Bifunctor<L,R,Either<?,?>>

Specified by:

biMapL in interface BoundedBifunctor<L,R,java.lang.Object,java.lang.Object,Either<?,?>>

Type Parameters:

L2 - the new left parameter type

Parameters:

fn - the mapping function

Returns:

a bifunctor over C (the new left parameter) and B (the same right parameter)

biMapR

public final <R2> Either<L,R2> biMapR(Fn1<? super R,? extends R2> fn)

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

Specified by:

biMapR in interface Bifunctor<L,R,Either<?,?>>

Specified by:

biMapR in interface BoundedBifunctor<L,R,java.lang.Object,java.lang.Object,Either<?,?>>

Type Parameters:

R2 - the new right parameter type

Parameters:

fn - the mapping function

Returns:

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

biMap

public final <L2,R2> Either<L2,R2> biMap(Fn1<? super L,? extends L2> leftFn,
                                                     Fn1<? super R,? extends R2> rightFn)

Dually map covariantly over both the left and right parameters. This is isomorphic to biMapL(lFn).biMapR(rFn).

Specified by:

biMap in interface Bifunctor<L,R,Either<?,?>>

Specified by:

biMap in interface BoundedBifunctor<L,R,java.lang.Object,java.lang.Object,Either<?,?>>

Type Parameters:

L2 - the new left parameter type

R2 - the new right parameter type

Parameters:

leftFn - the left parameter mapping function

rightFn - the right parameter mapping function

Returns:

a bifunctor over C (the new left parameter type) and D (the new right parameter type)

pure

public final <R2> Either<L,R2> pure(R2 r2)

Lift the value b into this applicative functor.

Specified by:

pure in interface Applicative<L,R>

Specified by:

pure in interface Monad<L,R>

Specified by:

pure in interface MonadError<L,R,Either<L,?>>

Specified by:

pure in interface MonadRec<L,R>

Type Parameters:

R2 - the type of the returned applicative's parameter

Parameters:

r2 - the value

Returns:

an instance of this applicative over b

zip

public final <R2> Either<L,R2> zip(Applicative<Fn1<? super R,? extends R2>,Either<L,?>> 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<L,R>

Specified by:

zip in interface Monad<L,R>

Specified by:

zip in interface MonadError<L,R,Either<L,?>>

Specified by:

zip in interface MonadRec<L,R>

Type Parameters:

R2 - the resulting applicative parameter type

Parameters:

appFn - the other applicative instance

Returns:

the mapped applicative

lazyZip

public <R2> Lazy<Either<L,R2>> lazyZip(Lazy<? extends Applicative<Fn1<? super R,? extends R2>,Either<L,?>>> 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<L,R>

Specified by:

lazyZip in interface Monad<L,R>

Specified by:

lazyZip in interface MonadError<L,R,Either<L,?>>

Specified by:

lazyZip in interface MonadRec<L,R>

Type Parameters:

R2 - the resulting applicative parameter type

Parameters:

lazyAppFn - the lazy other applicative instance

Returns:

the mapped applicative

See Also:

Maybe, Either

discardL

public final <R2> Either<L,R2> discardL(Applicative<R2,Either<L,?>> 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<L,R>

Specified by:

discardL in interface Monad<L,R>

Specified by:

discardL in interface MonadError<L,R,Either<L,?>>

Specified by:

discardL in interface MonadRec<L,R>

Type Parameters:

R2 - the type of the returned Applicative's parameter

Parameters:

appB - the other Applicative

Returns:

appB

discardR

public final <R2> Either<L,R> discardR(Applicative<R2,Either<L,?>> 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<L,R>

Specified by:

discardR in interface Monad<L,R>

Specified by:

discardR in interface MonadError<L,R,Either<L,?>>

Specified by:

discardR in interface MonadRec<L,R>

Type Parameters:

R2 - the type of appB's parameter

Parameters:

appB - the other Applicative

Returns:

this Applicative

throwError

public Either<L,R> throwError(L l)

Throw an error value of type E into the monad.

Specified by:

throwError in interface MonadError<L,R,Either<L,?>>

Parameters:

l - the error type

Returns:

the monad

catchError

public Either<L,R> catchError(Fn1<? super L,? extends Monad<R,Either<L,?>>> recoveryFn)

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

Specified by:

catchError in interface MonadError<L,R,Either<L,?>>

Parameters:

recoveryFn - the catch function

Returns:

the recovered Monad

traverse

public final <R2,App extends Applicative<?,App>,TravB extends Traversable<R2,Either<L,?>>,AppTrav extends Applicative<TravB,App>> AppTrav traverse(Fn1<? super R,? extends Applicative<R2,App>> fn,
                                                                                                                                                                                             Fn1<? super TravB,? extends AppTrav> pure)

Apply fn to each element of this traversable from left to right, and collapse the results into a single resulting applicative, potentially with the assistance of the applicative's pure function.

Specified by:

traverse in interface Traversable<L,R>

Type Parameters:

R2 - the resulting element type

App - the result applicative type

TravB - this Traversable instance over B

AppTrav - the full inferred resulting type from the traversal

Parameters:

fn - the function to apply

pure - the applicative pure function

Returns:

the traversed Traversable, wrapped inside an applicative

toMaybe

public final Maybe<R> toMaybe()

In the left case, returns a Maybe.nothing(); otherwise, returns Maybe.maybe(A) around the right value.

Returns:

Maybe the right value

fromMaybe

public static <L,R> Either<L,R> fromMaybe(Maybe<R> maybe,
                                                      Fn0<L> leftFn0)

Convert a Maybe<R> into an Either<L, R>, supplying the left value from leftFn in the case of Maybe.nothing().

Type Parameters:

L - the left parameter type

R - the right parameter type

Parameters:

maybe - the maybe

leftFn0 - the supplier to use for left values

Returns:

a right value of the contained maybe value, or a left value of leftFn's result

trying

public static <L,R> Either<L,R> trying(Fn0<? extends R> fn0,
                                                   Fn1<? super java.lang.Throwable,? extends L> leftFn)

Attempt to execute the Fn0, returning its result in a right value. If the supplier throws an exception, apply leftFn to it, wrap it in a left value and return it.

Type Parameters:

L - the left parameter type

R - the right parameter type

Parameters:

fn0 - the supplier of the right value

leftFn - a function mapping E to L

Returns:

the supplier result as a right value, or leftFn's mapping result as a left value

trying

public static <R> Either<java.lang.Throwable,R> trying(Fn0<? extends R> fn0)

Attempt to execute the Fn0, returning its result in a right value. If the supplier throws an exception, wrap it in a left value and return it.

Type Parameters:

R - the right parameter type

Parameters:

fn0 - the supplier of the right value

Returns:

the supplier result as a right value, or a left value of the thrown exception

trying

public static <L> Either<L,Unit> trying(SideEffect sideEffect,
                                              Fn1<? super java.lang.Throwable,? extends L> leftFn)

Attempt to execute the SideEffect, returning Unit in a right value. If the runnable throws an exception, apply leftFn to it, wrap it in a left value, and return it.

Type Parameters:

L - the left parameter type

Parameters:

sideEffect - the runnable

leftFn - a function mapping E to L

Returns:

Unit as a right value, or leftFn's mapping result as a left value

trying

public static Either<java.lang.Throwable,Unit> trying(SideEffect sideEffect)

Attempt to execute the SideEffect, returning Unit in a right value. If the runnable throws exception, wrap it in a left value and return it.

Parameters:

sideEffect - the runnable

Returns:

Unit as a right value, or a left value of the thrown exception

left

public static <L,R> Either<L,R> left(L l)

Static factory method for creating a left value.

Type Parameters:

L - the left parameter type

R - the right parameter type

Parameters:

l - the wrapped value

Returns:

a left value of l

right

public static <L,R> Either<L,R> right(R r)

Static factory method for creating a right value.

Type Parameters:

L - the left parameter type

R - the right parameter type

Parameters:

r - the wrapped value

Returns:

a right value of r

pureEither

public static <L> Pure<Either<L,?>> pureEither()

The canonical Pure instance for Either.

Type Parameters:

L - the left type

Returns:

the Pure instance