Class Const<A,B>

java.lang.Object
com.jnape.palatable.lambda.functor.builtin.Const<A,B>
Type Parameters:
A - the left parameter type, and the type of the stored value
B - the right (phantom) parameter type
All Implemented Interfaces:
Applicative<B, Const<A,?>>, Bifunctor<A, B, Const<?,?>>, BoundedBifunctor<A, B, Object, Object, Const<?,?>>, Functor<B, Const<A,?>>, Monad<B, Const<A,?>>, MonadRec<B, Const<A,?>>, Traversable<B, Const<A,?>>
public final class Const<A,B> extends Object implements MonadRec<B, Const<A,?>>, Bifunctor<A, B, Const<?,?>>, Traversable<B, Const<A,?>>
A (surprisingly useful) functor over some phantom type B, retaining a value of type A that can be retrieved later. This is useful in situations where it is desirable to retain constant information throughout arbitrary functor transformations, such that at the end of the chain, regardless of how B has been altered, A is still pristine and retrievable.

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    private final A
    a
     

  • Constructor Summary

    Constructors
    Constructor
    Description
    Const(A a)
     

  • Method Summary

    Modifier and Type
    Method
    Description
    <C,D> Const<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.
    <Z> Const<Z,B>
    biMapL(Fn1<? super A, ? extends Z> fn)
    Covariantly map over the left parameter.
    <C> Const<A,C>
    biMapR(Fn1<? super B, ? extends C> fn)
    Covariantly map over the right parameter.
    <C> Const<A,C>
    discardL(Applicative<C, Const<A,?>> appB)
    Sequence both this Applicative and appB, discarding this Applicative's result and returning appB.
    <C> Const<A,B>
    discardR(Applicative<C, Const<A,?>> appB)
    Sequence both this Applicative and appB, discarding appB's result and returning this Applicative.
    boolean
    equals(Object other)
     
    <C> Const<A,C>
    flatMap(Fn1<? super B, ? extends Monad<C, Const<A,?>>> f)
    Chain dependent computations that may continue or short-circuit based on previous results.
    <C> Const<A,C>
    fmap(Fn1<? super B, ? extends C> fn)
    Map over the right parameter.
    int
    hashCode()
     
    <C> Lazy<Const<A,C>>
    lazyZip(Lazy<? extends Applicative<Fn1<? super B, ? extends C>, Const<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.
    <C> Const<A,C>
    pure(C c)
    Lift the value b into this applicative functor.
    static <A> Pure<Const<A,?>>
    pureConst(A a)
    The canonical Pure instance for Const.
    A
    runConst()
    Retrieve the stored value.
    String
    toString()
     
    <C> Const<A,C>
    trampolineM(Fn1<? super B, ? extends MonadRec<RecursiveResult<B,C>, Const<A,?>>> fn)
    Given some operation yielding a RecursiveResult inside this MonadRec, internally trampoline the operation until it yields a termination instruction.
    <C, App extends Applicative<?,App>, TravB extends Traversable<C, Const<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.
    <C> Const<A,C>
    zip(Applicative<Fn1<? super B, ? extends C>, Const<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.

    Methods inherited from class Object

    clone, finalize, getClass, notify, notifyAll, wait, wait, wait

    Methods inherited from interface Functor

    coerce

  • Field Details

    • a

      private final A a

  • Constructor Details

    • Const

      public Const(A a)

  • Method Details

    • runConst

      public A runConst()
      Retrieve the stored value.
      Returns:
      the value

    • fmap

      public <C> Const<A,C> fmap(Fn1<? super B, ? extends C> fn)
      Map over the right parameter. Note that because B is never actually known quantity outside of a type signature, this is effectively a no-op that serves only to alter Const's type signature.
      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 right parameter type
      Parameters:
      fn - the mapping function
      Returns:
      a Const over A (the same value) and C (the new phantom parameter)

    • pure

      public <C> Const<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> Const<A,C> zip(Applicative<Fn1<? super B, ? extends C>, Const<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<Const<A,C>> lazyZip(Lazy<? extends Applicative<Fn1<? super B, ? extends C>, Const<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> Const<A,C> discardL(Applicative<C, Const<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> Const<A,B> discardR(Applicative<C, Const<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 <C> Const<A,C> flatMap(Fn1<? super B, ? extends Monad<C, Const<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> Const<A,C> trampolineM(Fn1<? super B, ? extends MonadRec<RecursiveResult<B,C>, Const<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, Const<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

    • biMapL

      public <Z> Const<Z,B> biMapL(Fn1<? super A, ? extends Z> fn)
      Covariantly map over the left parameter.
      Specified by:
      biMapL in interface Bifunctor<A, B, Const<?,?>>
      Specified by:
      biMapL in interface BoundedBifunctor<A, B, Object, Object, Const<?,?>>
      Type Parameters:
      Z - 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 <C> Const<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, Const<?,?>>
      Specified by:
      biMapR in interface BoundedBifunctor<A, B, Object, Object, Const<?,?>>
      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 <C,D> Const<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, Const<?,?>>
      Specified by:
      biMap in interface BoundedBifunctor<A, B, Object, Object, Const<?,?>>
      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)

    • 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

    • pureConst

      public static <A> Pure<Const<A,?>> pureConst(A a)
      The canonical Pure instance for Const.
      Type Parameters:
      A - the left parameter type, and the type of the stored value
      Parameters:
      a - the stored value
      Returns:
      the Pure instance