core/functional/src/docs/functional.txt

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[[core-functional,Function]]
= Core Functional API =

[devstatus]
--------------
source=core/functional/dev-status.xml
--------------

The Qi4j Core Functional API is a generic package to work with Iterables in a "functional programming language" style.

This package is completely independent of everything else in Qi4j and may be used on its own in any kind of environment
such as Spring or Java EE applications.

== First Example ==
Let's say that you have an Iterable of Integers and you want to sum them all up. Most people would create a loop and
sum it all up in something like this;

[source,java]
-------------
Iterable<Integer> data = ...;

long sum = 0;
for( Long point : data ) {
    sum = sum + point;
}
System.out.println( "The sum is " + sum );
-------------

With the Qi4j Core Functional API, you go about it in a different way. The code ends up looking like this;

[source,java]
-------------
Iterable<Number> data = ...;
Long sum = forEach( data ).map( longSum() ).last();
System.out.println( "The sum is " + sum );
-------------

And this is just the tip of the iceberg.

== The Big Picture ==

The Qi4j Core Functional API are divided a handful of powerful concepts, especially when used together;

   * *Iterables* - many methods to deal with Iterable data, so that the loops in your programs can largely be removed.

   * *Functions* - f(x) and f(x,y) are well-know from mathematics and used in functional programming languages. Qi4j is
     not capable of introducing lambda calculus due to limitations in Java itself, but we can simulate a lot to allow
     people to create more readable code.

   * *Specification* - A simple concept to define the bounds of data. This is used for filtering, query and many other
     higher level abstractions.

   * *Visitor* pattern - A way to be handed the items in a collection, without having the loops. This could be for
     end result handling, distribution of intermediary values, and many other things.


== Specification ==
TODO

== Function ==
TODO

== Visitor Pattern ==
TODO

== Iterables ==
TODO