Class Choice2<A,B>

java.lang.Object
com.jnape.palatable.lambda.adt.choice.Choice2<A,B>
Type Parameters:
A - the first possible type
B - the second possible type
All Implemented Interfaces:
CoProduct2<A, B, Choice2<A,B>>, Applicative<B, Choice2<A,?>>, Bifunctor<A, B, Choice2<?,?>>, BoundedBifunctor<A, B, Object, Object, Choice2<?,?>>, Functor<B, Choice2<A,?>>, Monad<B, Choice2<A,?>>, MonadRec<B, Choice2<A,?>>, Traversable<B, Choice2<A,?>>
Direct Known Subclasses:
Choice2._A, Choice2._B
public abstract class Choice2<A,B> extends Object implements CoProduct2<A, B, Choice2<A,B>>, MonadRec<B, Choice2<A,?>>, Bifunctor<A, B, Choice2<?,?>>, Traversable<B, Choice2<A,?>>
Canonical ADT representation of CoProduct2. Unlike Either, there is no concept of "success" or "failure", so the domain of reasonable function semantics is more limited.
See Also:

  • Constructor Details

    • Choice2

      private Choice2()

  • Method Details

    • project

      public Tuple2<Maybe<A>,Maybe<B>> project()
      Specialize this choice's projection to a Tuple2.
      Specified by:
      project in interface CoProduct2<A, B, Choice2<A,B>>
      Returns:
      a Tuple2

    • diverge

      public final <C> Choice3<A,B,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(Fn1, Fn1), 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<A, B, Choice2<A,B>>
      Type Parameters:
      C - the additional possible type of this coproduct
      Returns:
      a CoProduct3<A, B, C>

    • invert

      public Choice2<B,A> invert()
      Swap the type parameters.
      Specified by:
      invert in interface CoProduct2<A, B, Choice2<A,B>>
      Returns:
      The inverted coproduct

    • fmap

      public final <C> Choice2<A,C> fmap(Fn1<? super B, ? extends C> 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<A,B>
      Specified by:
      fmap in interface Functor<A,B>
      Specified by:
      fmap in interface Monad<A,B>
      Specified by:
      fmap in interface MonadRec<A,B>
      Specified by:
      fmap in interface Traversable<A,B>
      Type Parameters:
      C - the new parameter type
      Parameters:
      fn - the mapping function
      Returns:
      a functor over B (the new parameter type)

    • biMapL

      public final <C> Choice2<C,B> biMapL(Fn1<? super A, ? extends C> fn)
      Covariantly map over the left parameter.
      Specified by:
      biMapL in interface Bifunctor<A, B, Choice2<?,?>>
      Specified by:
      biMapL in interface BoundedBifunctor<A, B, Object, Object, Choice2<?,?>>
      Type Parameters:
      C - 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 <C> Choice2<A,C> biMapR(Fn1<? super B, ? extends C> 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<A, B, Choice2<?,?>>
      Specified by:
      biMapR in interface BoundedBifunctor<A, B, Object, Object, Choice2<?,?>>
      Type Parameters:
      C - 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 <C,D> Choice2<C,D> biMap(Fn1<? super A, ? extends C> lFn, Fn1<? super B, ? extends D> rFn)
      Dually map covariantly over both the left and right parameters. This is isomorphic to biMapL(lFn).biMapR(rFn).
      Specified by:
      biMap in interface Bifunctor<A, B, Choice2<?,?>>
      Specified by:
      biMap in interface BoundedBifunctor<A, B, Object, Object, Choice2<?,?>>
      Type Parameters:
      C - the new left parameter type
      D - the new right parameter type
      Parameters:
      lFn - the left parameter mapping function
      rFn - the right parameter mapping function
      Returns:
      a bifunctor over C (the new left parameter type) and D (the new right parameter type)

    • pure

      public <C> Choice2<A,C> pure(C c)
      Lift the value b into this applicative functor.
      Specified by:
      pure in interface Applicative<A,B>
      Specified by:
      pure in interface Monad<A,B>
      Specified by:
      pure in interface MonadRec<A,B>
      Type Parameters:
      C - the type of the returned applicative's parameter
      Parameters:
      c - the value
      Returns:
      an instance of this applicative over b

    • zip

      public <C> Choice2<A,C> zip(Applicative<Fn1<? super B, ? extends C>, Choice2<A,?>> 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<A,B>
      Specified by:
      zip in interface Monad<A,B>
      Specified by:
      zip in interface MonadRec<A,B>
      Type Parameters:
      C - the resulting applicative parameter type
      Parameters:
      appFn - the other applicative instance
      Returns:
      the mapped applicative

    • lazyZip

      public <C> Lazy<Choice2<A,C>> lazyZip(Lazy<? extends Applicative<Fn1<? super B, ? extends C>, Choice2<A,?>>> 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<A,B>
      Specified by:
      lazyZip in interface Monad<A,B>
      Specified by:
      lazyZip in interface MonadRec<A,B>
      Type Parameters:
      C - the resulting applicative parameter type
      Parameters:
      lazyAppFn - the lazy other applicative instance
      Returns:
      the mapped applicative
      See Also:

    • discardL

      public <C> Choice2<A,C> discardL(Applicative<C, Choice2<A,?>> 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<A,B>
      Specified by:
      discardL in interface Monad<A,B>
      Specified by:
      discardL in interface MonadRec<A,B>
      Type Parameters:
      C - the type of the returned Applicative's parameter
      Parameters:
      appB - the other Applicative
      Returns:
      appB

    • discardR

      public <C> Choice2<A,B> discardR(Applicative<C, Choice2<A,?>> 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<A,B>
      Specified by:
      discardR in interface Monad<A,B>
      Specified by:
      discardR in interface MonadRec<A,B>
      Type Parameters:
      C - the type of appB's parameter
      Parameters:
      appB - the other Applicative
      Returns:
      this Applicative

    • flatMap

      public final <C> Choice2<A,C> flatMap(Fn1<? super B, ? extends Monad<C, Choice2<A,?>>> f)
      Chain dependent computations that may continue or short-circuit based on previous results.
      Specified by:
      flatMap in interface Monad<A,B>
      Specified by:
      flatMap in interface MonadRec<A,B>
      Type Parameters:
      C - the resulting monad parameter type
      Parameters:
      f - the dependent computation over A
      Returns:
      the new monad instance

    • trampolineM

      public <C> Choice2<A,C> trampolineM(Fn1<? super B, ? extends MonadRec<RecursiveResult<B,C>, Choice2<A,?>>> 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<A,B>
      Type Parameters:
      C - the ultimate resulting carrier type
      Parameters:
      fn - the function to internally trampoline
      Returns:
      the trampolined MonadRec
      See Also:

    • traverse

      public <C, App extends Applicative<?,App>, TravB extends Traversable<C, Choice2<A,?>>, AppTrav extends Applicative<TravB,App>> AppTrav traverse(Fn1<? super B, ? extends Applicative<C,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<A,B>
      Type Parameters:
      C - 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

    • a

      public static <A,B> Choice2<A,B> a(A a)
      Static factory method for wrapping a value of type A in a Choice2.
      Type Parameters:
      A - the first possible type
      B - the second possible type
      Parameters:
      a - the value
      Returns:
      the wrapped value as a Choice2<A, B>

    • b

      public static <A,B> Choice2<A,B> b(B b)
      Static factory method for wrapping a value of type B in a Choice2.
      Type Parameters:
      A - the first possible type
      B - the second possible type
      Parameters:
      b - the value
      Returns:
      the wrapped value as a Choice2<A, B>

    • pureChoice

      public static <A> Pure<Choice2<A,?>> pureChoice()
      The canonical Pure instance for Choice2.
      Type Parameters:
      A - the first possible type
      Returns:
      the Pure instance