pure.java

All codes tested on this playground.

Diffs

There will be something defferect in Java.

Closures

We mock a closure with method inner an Anonymous Sub-Class.

What we cannot

In Java you can't write a value like that:

<A> Function<A, A> idiot = a -> a ; /// err
var idiot = (<A> Function<A, A>) (a -> a) ; /// err

You can just:

<A> A idiot (A a) { return a ; }

/// or
final var birds = 
new Object() 
{
    <A> A idiot (A a) { return a ; }
} ;

birds.idiot(7) ; // 7

So what we can

The generic just allowed at method but not a lambda.

So, we can just let the method be a value !!

Like these:

For normal way

we define:

final var things = 
new Object() 
{
	Integer a = 7 ;
	String b = "bzzzz" ;
	<A> Function<A,A> idi = (<A> Function<A,A>) (a -> a) ;
} ;

and want:

things.a ; // 7
things.b ; // "bzzzz"
things.idi.apply(things.a) ; // 7
things.idi.apply(things.b) ; // "bzzzz"

but we cannot, because the <A> Function<A,A> idi = (Function<A,A>) (a -> a) ; is unsupported in Java (yet now), it will give error because of this line.

But we can do things like that now: all method just use to return a value.

Like that:

Our new way here

final var things = 
new Object() 
{
	Integer a () { return 7 ;}
	String b () { return "bzzzz" ;}
	<A> Function<A,A> idi () { return (Function<A,A>) (a -> a) ;}
} ;

And then so we can use:

things.a() ; // 7
things.b() ; // "bzzzz"
things.idi().apply(things.a()) ; // 7
things.idi().apply(things.b()) ; // "bzzzz"

Things is done !!

And that's all given by anonymous (sub)classes' supports in Java.

(Or we can also just ...)

final var things = 
new Object() 
{
	Integer a = 7 ;
	String b = "bzzzz" ;
	<A> Function<A,A> idi () { return (Function<A,A>) (a -> a) ;}
} ;

things.a ; // 7
things.b ; // "bzzzz"
things.idi().apply(things.a) ; // 7
things.idi().apply(things.b) ; // "bzzzz"

... means only lambda values into method style.

Namespaces

Or called modules. That is simple, also a new Object () {...}, we have no necessary to use a IIFE even ...

Types

I don't know how to define (or mock) a recursive type in Java yet ...