com.jnape.palatable.lambda.optics.lenses

Class MaybeLens

java.lang.Object

com.jnape.palatable.lambda.optics.lenses.MaybeLens

public final class MaybeLens
extends Object

Lenses that operate on Maybe.

Method Summary

Modifier and Type	Method and Description
static <V> Lens.Simple<V,Maybe<V>>	asMaybe() Convenience static factory method for creating a lens that focuses on a value as a Maybe.
static <S,T,A,B> Lens<S,T,Maybe<A>,B>	liftA(Lens<S,T,A,B> lens) Given a lens, lift A into Maybe.
static <S,T,A,B> Lens<S,T,A,Maybe<B>>	liftB(Lens<S,T,A,B> lens, B defaultB) Given a lens and a default B, lift B into Maybe.
static <S,T,A,B> Lens<Maybe<S>,T,A,B>	liftS(Lens<S,T,A,B> lens, S defaultS) Given a lens and a default S, lift S into Maybe.
static <S,T,A,B> Lens<S,Maybe<T>,A,B>	liftT(Lens<S,T,A,B> lens) Given a lens, lift T into Maybe.
static <S,T,A,B> Lens<S,T,A,B>	unLiftA(Lens<S,T,Maybe<A>,B> lens, A defaultA) Given a lens with A lifted into Maybe and a default A, flatten A back down.
static <S,T,A,B> Lens<S,T,A,B>	unLiftB(Lens<S,T,A,Maybe<B>> lens) Given a lens with B lifted into Maybe, flatten B back down.
static <S,T,A,B> Lens<S,T,A,B>	unLiftS(Lens<Maybe<S>,T,A,B> lens) Given a lens with S lifted into Maybe, flatten S back down.
static <S,T,A,B> Lens<S,T,A,B>	unLiftT(Lens<S,Maybe<T>,A,B> lens, T defaultT) Given a lens with T lifted into Maybe and a default T, flatten T back down.

Methods inherited from class java.lang.Object

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

Method Detail

liftS

public static <S,T,A,B> Lens<Maybe<S>,T,A,B> liftS(Lens<S,T,A,B> lens,
                                                   S defaultS)

Given a lens and a default S, lift S into Maybe.

Note that this lens is NOT lawful, since "putting back what you got changes nothing" fails for any value B where S is Maybe.nothing().

Type Parameters:

S - the type of the "larger" value for reading

T - the type of the "larger" value for putting

A - the type of the "smaller" value that is read

B - the type of the "smaller" update value

Parameters:

lens - the lens

defaultS - the S to use if Maybe.nothing() is given

Returns:

the lens with S lifted

liftT

public static <S,T,A,B> Lens<S,Maybe<T>,A,B> liftT(Lens<S,T,A,B> lens)

Given a lens, lift T into Maybe.

Type Parameters:

S - the type of the "larger" value for reading

T - the type of the "larger" value for putting

A - the type of the "smaller" value that is read

B - the type of the "smaller" update value

Parameters:

lens - the lens

Returns:

the lens with T lifted

liftA

public static <S,T,A,B> Lens<S,T,Maybe<A>,B> liftA(Lens<S,T,A,B> lens)

Given a lens, lift A into Maybe.

Type Parameters:

S - the type of the "larger" value for reading

T - the type of the "larger" value for putting

A - the type of the "smaller" value that is read

B - the type of the "smaller" update value

Parameters:

lens - the lens

Returns:

the lens with A lifted

liftB

public static <S,T,A,B> Lens<S,T,A,Maybe<B>> liftB(Lens<S,T,A,B> lens,
                                                   B defaultB)

Given a lens and a default B, lift B into Maybe.

Note that this lens is NOT lawful, since "putting back what you got changes nothing" fails for any value B where S is Maybe.nothing().

Type Parameters:

S - the type of the "larger" value for reading

T - the type of the "larger" value for putting

A - the type of the "smaller" value that is read

B - the type of the "smaller" update value

Parameters:

lens - the lens

defaultB - the B to use if Maybe.nothing() is given

Returns:

the lens with B lifted

unLiftS

public static <S,T,A,B> Lens<S,T,A,B> unLiftS(Lens<Maybe<S>,T,A,B> lens)

Given a lens with S lifted into Maybe, flatten S back down.

Type Parameters:

S - the type of the "larger" value for reading

T - the type of the "larger" value for putting

A - the type of the "smaller" value that is read

B - the type of the "smaller" update value

Parameters:

lens - the lens

Returns:

the lens with S flattened

unLiftT

public static <S,T,A,B> Lens<S,T,A,B> unLiftT(Lens<S,Maybe<T>,A,B> lens,
                                              T defaultT)

Given a lens with T lifted into Maybe and a default T, flatten T back down.

Note that while this lens is not *necessarily* unlawful, it probably is, since the only case where "you get back what you put in" would not be violated is if T could never be Maybe.nothing().

Type Parameters:

S - the type of the "larger" value for reading

T - the type of the "larger" value for putting

A - the type of the "smaller" value that is read

B - the type of the "smaller" update value

Parameters:

lens - the lens

defaultT - the T to use if lens produces Maybe.nothing()

Returns:

the lens with T flattened

unLiftA

public static <S,T,A,B> Lens<S,T,A,B> unLiftA(Lens<S,T,Maybe<A>,B> lens,
                                              A defaultA)

Given a lens with A lifted into Maybe and a default A, flatten A back down.

Note that while this lens is not *necessarily* unlawful, it probably is, since the only case where "putting back what you got changes nothing" would not be violated is if A could never be Maybe.nothing().

Type Parameters:

S - the type of the "larger" value for reading

T - the type of the "larger" value for putting

A - the type of the "smaller" value that is read

B - the type of the "smaller" update value

Parameters:

lens - the lens

defaultA - the A to use if lens produces Maybe.nothing()

Returns:

the lens with A flattened

unLiftB

public static <S,T,A,B> Lens<S,T,A,B> unLiftB(Lens<S,T,A,Maybe<B>> lens)

Given a lens with B lifted into Maybe, flatten B back down.

Type Parameters:

S - the type of the "larger" value for reading

T - the type of the "larger" value for putting

A - the type of the "smaller" value that is read

B - the type of the "smaller" update value

Parameters:

lens - the lens

Returns:

the lens with B flattened

asMaybe

public static <V> Lens.Simple<V,Maybe<V>> asMaybe()

Convenience static factory method for creating a lens that focuses on a value as a Maybe.

Type Parameters:

V - the value type

Returns:

a lens that focuses on the value as a Maybe