cyclops.companion

Class Optionals.Instances

java.lang.Object

cyclops.companion.Optionals.Instances

Enclosing class:

Optionals

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

Companion class for creating Type Class instances for working with Optionals

Constructor Summary

Constructors

Constructor and Description
Instances()

Method Summary

Modifier and Type	Method and Description
static <T,R> Applicative<Witness.optional>	applicative() import static com.aol.cyclops.hkt.jdk.OptionalKind.widen; import static com.aol.cyclops.util.function.Lambda.l1; import static java.util.Arrays.asOptional; Optionals.zippingApplicative() .ap(widen(asOptional(l1(this::multiplyByTwo))),widen(asOptional(1,2,3))); //[2,4,6]
static <T> Comonad<Witness.optional>	comonad()
static InstanceDefinitions<Witness.optional>	definitions()
static <T,R> Foldable<Witness.optional>	foldable() int sum = Optionals.foldable() .foldLeft(0, (a,b)->a+b, OptionalKind.widen(Arrays.asOptional(1,2,3,4))); //10
static <T,R> Functor<Witness.optional>	functor() Transform a list, mulitplying every element by 2
static <T,R> Monad<Witness.optional>	monad() import static com.aol.cyclops.hkt.jdk.OptionalKind.widen; OptionalKind<Integer> list = Optionals.monad() .flatMap(i->widen(OptionalX.range(0,i)), widen(Arrays.asOptional(1,2,3))) .convert(OptionalKind::narrowK3);
static <T> MonadPlus<Witness.optional>	monadPlus() OptionalKind<Integer> list = Optionals.<Integer>monadPlus() .plus(OptionalKind.widen(Arrays.asOptional()), OptionalKind.widen(Arrays.asOptional(10))) .convert(OptionalKind::narrowK3); //Arrays.asOptional(10))
static <T> MonadPlus<Witness.optional>	monadPlus(Monoid<Optionals.OptionalKind<T>> m) Monoid<OptionalKind<Integer>> m = Monoid.of(OptionalKind.widen(Arrays.asOptional()), (a,b)->a.isEmpty() ? b : a); OptionalKind<Integer> list = Optionals.<Integer>monadPlus(m) .plus(OptionalKind.widen(Arrays.asOptional(5)), OptionalKind.widen(Arrays.asOptional(10))) .convert(OptionalKind::narrowK3); //Arrays.asOptional(5))
static MonadRec<Witness.optional>	monadRec()
static <T,R> MonadZero<Witness.optional>	monadZero() OptionalKind<String> list = Optionals.unit() .unit("hello") .applyHKT(h->Optionals.monadZero().filter((String t)->t.startsWith("he"), h)) .convert(OptionalKind::narrowK3); //Arrays.asOptional("hello"));
static <C2,T> Traverse<Witness.optional>	traverse()
static <T> Pure<Witness.optional>	unit() OptionalKind<String> list = Optionals.unit() .unit("hello") .convert(OptionalKind::narrowK3); //Arrays.asOptional("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

definitions

public static InstanceDefinitions<Witness.optional> definitions()

functor

public static <T,R> Functor<Witness.optional> functor()

Transform a list, mulitplying every element by 2

 
  OptionalKind<Integer> list = Optionals.functor().map(i->i*2, OptionalKind.widen(Arrays.asOptional(1,2,3));

  //[2,4,6]


 
 

An example fluent api working with Optionals

 
   OptionalKind<Integer> list = Optionals.unit()
        .unit("hello")
        .applyHKT(h->Optionals.functor().map((String v) ->v.length(), h))
        .convert(OptionalKind::narrowK3);

 
 

Returns:

A functor for Optionals

unit

public static <T> Pure<Witness.optional> unit()

 
 OptionalKind<String> list = Optionals.unit()
        .unit("hello")
        .convert(OptionalKind::narrowK3);

        //Arrays.asOptional("hello"))

 
 

Returns:

A factory for Optionals

applicative

public static <T,R> Applicative<Witness.optional> applicative()

 
 import static com.aol.cyclops.hkt.jdk.OptionalKind.widen;
 import static com.aol.cyclops.util.function.Lambda.l1;
 import static java.util.Arrays.asOptional;

        Optionals.zippingApplicative()
        .ap(widen(asOptional(l1(this::multiplyByTwo))),widen(asOptional(1,2,3)));

 //[2,4,6]
 
 

Example fluent API

 
 OptionalKind<Function<Integer,Integer>> listFn =Optionals.unit()
                                                  .unit(Lambda.l1((Integer i) ->i*2))
                                                  .convert(OptionalKind::narrowK3);

        OptionalKind<Integer> list = Optionals.unit()
        .unit("hello")
        .applyHKT(h->Optionals.functor().map((String v) ->v.length(), h))
        .applyHKT(h->Optionals.applicative().ap(listFn, h))
        .convert(OptionalKind::narrowK3);

        //Arrays.asOptional("hello".length()*2))

 
 

Returns:

A zipper for Optionals

monad

public static <T,R> Monad<Witness.optional> monad()

 
 import static com.aol.cyclops.hkt.jdk.OptionalKind.widen;
 OptionalKind<Integer> list  = Optionals.monad()
        .flatMap(i->widen(OptionalX.range(0,i)), widen(Arrays.asOptional(1,2,3)))
        .convert(OptionalKind::narrowK3);
 
 

Example fluent API

 
    OptionalKind<Integer> list = Optionals.unit()
        .unit("hello")
        .applyHKT(h->Optionals.monad().flatMap((String v) ->Optionals.unit().unit(v.length()), h))
        .convert(OptionalKind::narrowK3);

        //Arrays.asOptional("hello".length())

 
 

Returns:

Type class with monad functions for Optionals

monadZero

public static <T,R> MonadZero<Witness.optional> monadZero()

 
  OptionalKind<String> list = Optionals.unit()
        .unit("hello")
        .applyHKT(h->Optionals.monadZero().filter((String t)->t.startsWith("he"), h))
        .convert(OptionalKind::narrowK3);

        //Arrays.asOptional("hello"));

 
 

Returns:

A filterable monad (with default value)

monadRec

public static MonadRec<Witness.optional> monadRec()

monadPlus

public static <T> MonadPlus<Witness.optional> monadPlus()

 
  OptionalKind<Integer> list = Optionals.<Integer>monadPlus()
        .plus(OptionalKind.widen(Arrays.asOptional()), OptionalKind.widen(Arrays.asOptional(10)))
        .convert(OptionalKind::narrowK3);
        //Arrays.asOptional(10))

 
 

Returns:

Type class for combining Optionals by concatenation

monadPlus

public static <T> MonadPlus<Witness.optional> monadPlus(Monoid<Optionals.OptionalKind<T>> m)

 
  Monoid<OptionalKind<Integer>> m = Monoid.of(OptionalKind.widen(Arrays.asOptional()), (a,b)->a.isEmpty() ? b : a);
        OptionalKind<Integer> list = Optionals.<Integer>monadPlus(m)
        .plus(OptionalKind.widen(Arrays.asOptional(5)), OptionalKind.widen(Arrays.asOptional(10)))
        .convert(OptionalKind::narrowK3);
        //Arrays.asOptional(5))

 
 

Parameters:

m - Monoid to use for combining Optionals

Returns:

Type class for combining Optionals

traverse

public static <C2,T> Traverse<Witness.optional> traverse()

Returns:

Type class for traversables with traverse / sequence operations

foldable

public static <T,R> Foldable<Witness.optional> foldable()

 
 int sum  = Optionals.foldable()
        .foldLeft(0, (a,b)->a+b, OptionalKind.widen(Arrays.asOptional(1,2,3,4)));

        //10

 
 

Returns:

Type class for folding / reduction operations

comonad

public static <T> Comonad<Witness.optional> comonad()