functional.md

Functional

Overview

Functional

The Functional is a global instance to deal with functional methods. In general, when you use a method of some object in pipeline, you should do it as a following example.

obj |> { &(obj) => obj.map({ => _1 * 2 }) }
    |> { &(obj) => obj.method() }
    |> // ... and so on.

The Functional instance will wrap the actual function object and pass it into the pipeline. For example, you can write it as follows against the example above.

obj |> Functional.map { => _1 * 2 }
    |> Functional.method()  // Note that it needs a `()` to use an actual function object
                            // which receives an object at a first argument.
    |> // ... and so on.

Enumerable

The Enumerable is not only as a module but also a global instance having functional enumerable methods which is useful in a pipeline. For example, when multiple values are passed to the next function via pipeline, a method in Enumerable can fetch a value one by one and pass the value to a next function in order.

Therefore, Enumerable can handle an infinite sequence. This is an example below.

1..
    |> Functional.enumerable
    |> Enumerable.drop(10)
    |> Enumerable.filter { => _1 % 3 == 0 }
    |> Enumerable.take(10)
    |> Enumerable.toArray
    |> System.println;

The Functional.enumerable is a magic function to make a sequence change to an item which Enumerable methods can use. You can write it also like an example below, but the way how to write in the above example is more useful.

new Functional.Enumerator(1..)
    |> Enumerable.drop(10)
    |> Enumerable.filter { => _1 % 3 == 0 }
    |> Enumerable.take(10)
    |> Enumerable.toArray
    |> System.println;

Methods

The methods of Enumerable to pass values in pipeline is currently as follows.

Name	Outline
filter(func)	Filters by the element returned by func.
map(func)	Maps by the element returned by func.
flatMap(func)	Maps by the element returned by func, then flatten the all result.
take(n)	Takes n elements from the beginning.
takeWhile(func)	Takes an element while returning true by func.
drop(n)	Skips n elements from the beginning.
dropWhile(func)	Skips an element while returning true by func.
sort(func)	Sorts elements by comparing with the result of func. Note that this method will fetch all at first to sort.
shuffle(func)	Shuffles elements in an array. Note that this method will fetch all at first to shuffle.
each(func)	Applies func for each. The value will be passed to the next as it is.
println/println(msg)	Prints the value and pass it to the next. This is used to see inside the pipeline. msg can be lead message of output.

The following methods will aggregate a sequence. By one of those, the pipeline will be terminated once and a value will be aggregated.

Name	Outline
reduce(func, initer)	Reduces by the result of func. initer is the initial value if necessary.
all(func)	true if the result of func is all true for all elements.
any(func)	true if there is at least one element which is true returned by func.
sum	Returns a sum of all sequence items.
toArray	Returns gathered elements as Array.
partition(func)	Returns an array of 2 groups of a group which is returning true by func and a group which is returning false by func.
printlnAll	Apply System.println for all elements.

Enumerable.trace

This is not a functional method but a method just to trace and display items passed in the pipeline. This method will display an item and pass it to the next as it is.

Therefore, Enumerable.trace can be used before Functional.enumerable as an example below.

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
    |> Enumerable.trace
    |> Functional.enumerable
    |> Enumerable.each { => Enumerable.trace(_1) }
    |> Enumerable.reduce(&(r, e) => r += e, 0)
    |> Enumerable.trace
    ;

// [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
// 1
// 2
// 3
// 4
// 5
// 6
// 7
// 8
// 9
// 10
// 55

Examples

Example 1. Functional.Enumerator

Code

var $E = Enumerable;
var println = System.println;
var printlnArray = $E.toArray +> println;

new Functional.Enumerator(1..10)
    |> $E.filter({ => _1 <= 4 })
    |> $E.map({ => _1 * 10 })
    |> printlnArray;

Result

[10, 20, 30, 40]

Example 2. With Function Composition Operator

Code

var $E = Enumerable;
var println = System.println;
var printlnArray = $E.toArray +> println;

1..10
    |> Functional.enumerable
    |> $E.filter({ => _1 < 7 }) +> $E.map({ => _1 * 100 }) +> printlnArray
    ;

Result

[100, 200, 300, 400, 500, 600]

Example 3. dropWhile

Code

var $E = Enumerable;
var println = System.println;
var printlnArray = $E.toArray +> println;

1..20
    |> Functional.enumerable
    |> $E.dropWhile { => _1 < 10 || _1 % 2 == 0 }
    |> printlnArray;

Result

[11, 12, 13, 14, 15, 16, 17, 18, 19, 20]

Example 4. flatMap (1)

Code

var $E = Enumerable;
var println = System.println;
var printlnArray = $E.toArray +> println;

[[1, 2], [3, 4]]
    |> Functional.enumerable
    |> $E.flatMap { => _1.map { => _1 * 2 } }
    |> printlnArray;

Result

[2, 4, 6, 8]

Example 5. flatMap (2)

Code

var $E = Enumerable;
var println = System.println;
var printlnArray = $E.toArray +> println;

[10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
    |> Functional.enumerable
    |> $E.flatMap { => [_1, _1 * 2] }
    |> printlnArray;

Result

[10, 20, 9, 18, 8, 16, 7, 14, 6, 12, 5, 10, 4, 8, 3, 6, 2, 4, 1, 2, 0, 0]

Example 6. sort

Code

var $E = Enumerable;
var println = System.println;
var printlnArray = $E.toArray +> println;

[10, 21, 92, 22, 37, 23, 98, 76, 56 , 48, 88, 76, 109, 2, 54]
    |> $E.trace
    |> Functional.enumerable
    |> $E.shuffle
    |> printlnArray <+ $E.sort
    ;

Result

[10, 21, 92, 22, 37, 23, 98, 76, 56, 48, 88, 76, 109, 2, 54]
[2, 10, 21, 22, 23, 37, 48, 54, 56, 76, 76, 88, 92, 98, 109]

Example 7. Infinite Sequence

Code

var $E = Enumerable;
var println = System.println;
var printlnArray = $E.toArray +> println;

100..
    |> Functional.enumerable
    |> $E.println("==> ")
    |> $E.filter { => _1 % 2 == 0 }
    |> $E.println("filterred: ")
    |> $E.take(10)
    |> printlnArray;

Result

==> 100
filterred: 100
==> 101
==> 102
filterred: 102
==> 103
==> 104
filterred: 104
==> 105
==> 106
filterred: 106
==> 107
==> 108
filterred: 108
==> 109
==> 110
filterred: 110
==> 111
==> 112
filterred: 112
==> 113
==> 114
filterred: 114
==> 115
==> 116
filterred: 116
==> 117
==> 118
filterred: 118
[100, 102, 104, 106, 108, 110, 112, 114, 116, 118]

Example 8. all (1)

Code

var $E = Enumerable;
var println = System.println;

1..20
    |> Functional.enumerable
    |> $E.all({ => _1 > 0 })
    |> println;

Result

1

Example 9. all (2)

Code

var $E = Enumerable;
var println = System.println;

0..20
    |> Functional.enumerable
    |> $E.all({ => _1 < 20 })
    |> println;

Result

0

Example 10. all (3)

Code

var $E = Enumerable;
var println = System.println;

0...20
    |> Functional.enumerable
    |> $E.all({ => _1 < 20 })
    |> println;

Result

1

Example 11. any (1)

Code

var $E = Enumerable;
var println = System.println;

0..20
    |> Functional.enumerable
    |> $E.any({ => _1 >= 20 })
    |> println;

Result

1

Example 12. any (2)

Code

var $E = Enumerable;
var println = System.println;

0...20
    |> Functional.enumerable
    |> $E.any({ => _1 >= 20 })
    |> println;

Result

0

Example 13. sum

Code

var $E = Enumerable;
var println = System.println;
var printlnArray = $E.toArray +> println;

1..100
    |> Functional.enumerable
    |> $E.sum
    |> println;

Result

5050

Example 14. partition

Code

var $E = Enumerable;
var println = System.println;
var printlnArray = $E.toArray +> println;

[10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
    |> Functional.enumerable
    |> $E.partition { => _1 % 3 == 0 }
    |> Functional.enumerable
    |> $E.printlnAll;

Result

[9, 6, 3, 0]
[10, 8, 7, 5, 4, 2, 1]

Example 15. Example (1)

Code

1..
    |> Functional.enumerable
    |> Enumerable.drop(10)
    |> Enumerable.filter { => _1 % 3 == 0 }
    |> Enumerable.take(10)
    |> Enumerable.toArray
    |> System.println;

Result

[12, 15, 18, 21, 24, 27, 30, 33, 36, 39]

Example 16. Example (2)

Code

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
    |> Enumerable.trace
    |> Functional.enumerable
    |> Enumerable.each { => Enumerable.trace(_1) }
    |> Enumerable.reduce(&(r, e) => r += e, 0)
    |> Enumerable.trace
    ;

Result

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
1
2
3
4
5
6
7
8
9
10
55

Example 17. Functional (1)

Code

class Object(list_) {
    public map(func) {
        list_ = list_.map { => func(_) };
        return this;
    }
    public hoge() {
        list_ = list_ + list_;
        return this;
    }
    public value() {
        return list_;
    }
}

var r = new Object([1, 2, 3])
    |> Functional.map { => _ + 1 }
    |> Functional.map { => _ * 2 }
    |> Functional.hoge()    // to call methodMissing and register it, and use it.
    |> Functional.map { => _ * 2 }
    |> Functional.value()   // to call methodMissing and register it, and use it.
    ;
System.println(r); // [8, 12, 16, 8, 12, 16]

Result

[8, 12, 16, 8, 12, 16]

Example 18. Functional (2)

Code

var test = (1..10).toArray();
var r = test
    |> { => Array.map(_) { => _1 + ":" + _1 } }
    |> { => Array.map(_) { => String.split(_1, ":") } }
    |> Array.flatten
    ;
System.println(r);
var r = test
    |> Functional.map { => _1 + ":" + _1 }
    |> Functional.map { => String.split(_1, ":") }
    |> Array.flatten
    ;
System.println(r);

Result

["1", "1", "2", "2", "3", "3", "4", "4", "5", "5", "6", "6", "7", "7", "8", "8", "9", "9", "10", "10"]
["1", "1", "2", "2", "3", "3", "4", "4", "5", "5", "6", "6", "7", "7", "8", "8", "9", "9", "10", "10"]