cyclops.control

Class Maybe.Instances

java.lang.Object

cyclops.control.Maybe.Instances

Enclosing interface:

Maybe<T>

public static class Maybe.Instances
extends java.lang.Object

Companion class for creating Type Class instances for working with Maybes

Constructor Summary

Constructors

Constructor and Description
Instances()

Method Summary

Modifier and Type	Method and Description
static <T,R> Applicative<Maybe.µ>	applicative() import static com.aol.cyclops.hkt.jdk.Maybe.widen; import static com.aol.cyclops.util.function.Lambda.l1; import static java.util.Maybe.just; Maybes.zippingApplicative() .ap(widen(asMaybe(l1(this::multiplyByTwo))),widen(asMaybe(1,2,3))); //[2,4,6]
static <T> Comonad<Maybe.µ>	comonad()
static <T> Foldable<Maybe.µ>	foldable() int sum = Maybes.foldable() .foldLeft(0, (a,b)->a+b, Maybe.widen(Maybe.just(1))); //1
static <T,R> Functor<Maybe.µ>	functor() Transform a maybe, mulitplying every element by 2
static <T,R> Monad<Maybe.µ>	monad() import static com.aol.cyclops.hkt.jdk.Maybe.widen; Maybe<Integer> maybe = Maybes.monad() .flatMap(i->widen(MaybeX.range(0,i)), widen(Maybe.just(1,2,3))) .convert(Maybe::narrowK);
static <T> MonadPlus<Maybe.µ>	monadPlus() Maybe<Integer> maybe = Maybes.<Integer>monadPlus() .plus(Maybe.widen(Maybe.just()), Maybe.widen(Maybe.just(10))) .convert(Maybe::narrowK); //Maybe.just(10))
static <T> MonadPlus<Maybe.µ>	monadPlus(Monoid<Maybe<T>> m) Monoid<Maybe<Integer>> m = Monoid.of(Maybe.widen(Maybe.just()), (a,b)->a.isEmpty() ? b : a); Maybe<Integer> maybe = Maybes.<Integer>monadPlus(m) .plus(Maybe.widen(Maybe.just(5)), Maybe.widen(Maybe.just(10))) .convert(Maybe::narrowK); //Maybe[5]
static <T,R> MonadZero<Maybe.µ>	monadZero() Maybe<String> maybe = Maybes.unit() .unit("hello") .apply(h->Maybes.monadZero().filter((String t)->t.startsWith("he"), h)) .convert(Maybe::narrowK); //Maybe.just("hello"));
static <C2,T> Traverse<Maybe.µ>	traverse()
static <T> Pure<Maybe.µ>	unit() Maybe<String> maybe = Maybes.unit() .unit("hello") .convert(Maybe::narrowK); //Maybe.just("hello"))

Methods inherited from class java.lang.Object

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

Constructor Detail

Instances

public Instances()

Method Detail

functor

public static <T,R> Functor<Maybe.µ> functor()

Transform a maybe, mulitplying every element by 2

 
  Maybe<Integer> maybe = Maybes.functor().map(i->i*2, Maybe.widen(Maybe.just(1));

  //[2]


 
 

An example fluent api working with Maybes

 
   Maybe<Integer> maybe = Maybes.unit()
        .unit("hello")
        .apply(h->Maybes.functor().map((String v) ->v.length(), h))
        .convert(Maybe::narrowK);

 
 

Returns:

A functor for Maybes

unit

public static <T> Pure<Maybe.µ> unit()

 
 Maybe<String> maybe = Maybes.unit()
        .unit("hello")
        .convert(Maybe::narrowK);

        //Maybe.just("hello"))

 
 

Returns:

A factory for Maybes

applicative

public static <T,R> Applicative<Maybe.µ> applicative()

 
 import static com.aol.cyclops.hkt.jdk.Maybe.widen;
 import static com.aol.cyclops.util.function.Lambda.l1;
 import static java.util.Maybe.just;

        Maybes.zippingApplicative()
        .ap(widen(asMaybe(l1(this::multiplyByTwo))),widen(asMaybe(1,2,3)));

 //[2,4,6]
 
 

Example fluent API

 
 Maybe<Function<Integer,Integer>> maybeFn =Maybes.unit()
                                                  .unit(Lambda.l1((Integer i) ->i*2))
                                                  .convert(Maybe::narrowK);

        Maybe<Integer> maybe = Maybes.unit()
        .unit("hello")
        .apply(h->Maybes.functor().map((String v) ->v.length(), h))
        .apply(h->Maybes.applicative().ap(maybeFn, h))
        .convert(Maybe::narrowK);

        //Maybe.just("hello".length()*2))

 
 

Returns:

A zipper for Maybes

monad

public static <T,R> Monad<Maybe.µ> monad()

 
 import static com.aol.cyclops.hkt.jdk.Maybe.widen;
 Maybe<Integer> maybe  = Maybes.monad()
        .flatMap(i->widen(MaybeX.range(0,i)), widen(Maybe.just(1,2,3)))
        .convert(Maybe::narrowK);
 
 

Example fluent API

 
    Maybe<Integer> maybe = Maybes.unit()
        .unit("hello")
        .apply(h->Maybes.monad().flatMap((String v) ->Maybes.unit().unit(v.length()), h))
        .convert(Maybe::narrowK);

        //Maybe.just("hello".length())

 
 

Returns:

Type class with monad functions for Maybes

monadZero

public static <T,R> MonadZero<Maybe.µ> monadZero()

 
  Maybe<String> maybe = Maybes.unit()
        .unit("hello")
        .apply(h->Maybes.monadZero().filter((String t)->t.startsWith("he"), h))
        .convert(Maybe::narrowK);

        //Maybe.just("hello"));

 
 

Returns:

A filterable monad (with default value)

monadPlus

public static <T> MonadPlus<Maybe.µ> monadPlus()

 
  Maybe<Integer> maybe = Maybes.<Integer>monadPlus()
        .plus(Maybe.widen(Maybe.just()), Maybe.widen(Maybe.just(10)))
        .convert(Maybe::narrowK);
        //Maybe.just(10))

 
 

Returns:

Type class for combining Maybes by concatenation

monadPlus

public static <T> MonadPlus<Maybe.µ> monadPlus(Monoid<Maybe<T>> m)

 
  Monoid<Maybe<Integer>> m = Monoid.of(Maybe.widen(Maybe.just()), (a,b)->a.isEmpty() ? b : a);
        Maybe<Integer> maybe = Maybes.<Integer>monadPlus(m)
        .plus(Maybe.widen(Maybe.just(5)), Maybe.widen(Maybe.just(10)))
        .convert(Maybe::narrowK);
        //Maybe[5]

 
 

Parameters:

m - Monoid to use for combining Maybes

Returns:

Type class for combining Maybes

traverse

public static <C2,T> Traverse<Maybe.µ> traverse()

Returns:

Type class for traversables with traverse / sequence operations

foldable

public static <T> Foldable<Maybe.µ> foldable()

 
 int sum  = Maybes.foldable()
        .foldLeft(0, (a,b)->a+b, Maybe.widen(Maybe.just(1)));

        //1

 
 

Returns:

Type class for folding / reduction operations

comonad

public static <T> Comonad<Maybe.µ> comonad()