Class MaybeLens

java.lang.Object
com.jnape.palatable.lambda.optics.lenses.MaybeLens
public final class MaybeLens extends Object
Lenses that operate on Maybe.

  • Constructor Details

    • MaybeLens

      private MaybeLens()

  • Method Details

    • 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