https://github.com/farolfo/list-comprehensions-in-java

(college project, see jComprehension for the lib) Build sets in mathematical set-builder notation with Java, like { x * 2 | x E {1,2,3,4} ^ x is even }
https://github.com/farolfo/list-comprehensions-in-java

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(college project, see jComprehension for the lib) Build sets in mathematical set-builder notation with Java, like { x * 2 | x E {1,2,3,4} ^ x is even }

• Host: GitHub
• URL: https://github.com/farolfo/list-comprehensions-in-java
• Owner: farolfo
• License: mit
• Created: 2015-06-13T05:11:46.000Z (over 9 years ago)
• Default Branch: master
• Last Pushed: 2020-11-09T18:37:45.000Z (about 4 years ago)
• Last Synced: 2024-10-03T08:11:38.751Z (3 months ago)
• Language: Java
• Homepage:
• Size: 527 KB
• Stars: 9
• Watchers: 5
• Forks: 3
• Open Issues: 1
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# List Comprehensions in Java

Build lists in mathematical [set-builder notation](https://en.wikipedia.org/wiki/Set-builder_notation) with Java, like { x * 2 | x E {1,2} ^ x is even }.

Used at: :D https://github.com/farolfo/JComprehension

### Usage and motivation

In algebra we are able to define sets using set-builder notation, also known as set comprehension or list comprehension. For example, this computes the even numbers in a set of integers

```java

{ x | x E {1,2,3,4} ^ x is even }

// gives {2,4}

```

which is read as _give me the set of all x such that x belongs to {1,2,3,4} and x is even_.

But this notation jumped out of algebra and today we have ways to do this in [many](https://en.wikipedia.org/wiki/Comparison_of_programming_languages_(list_comprehension)) programming languages, such as Haskell or python.

Now you can achieve this in Java

```java

Predicate even = x -> x % 2 == 0;

List evens = new ListComprehension()

        .suchThat(x -> {

            x.belongsTo(Arrays.asList(1, 2, 3, 4));

            x.is(even);

        });

// evens = {2,4};

```

And if we want to transform the output expression in some way like

```java

{ x * 2 | x E {1,2,3,4} ^ x is even }

// gives {4,8}

```

Our java code would look like

```java

List duplicated = new ListComprehension()

        .giveMeAll((Integer x) -> x * 2)

        .suchThat(x -> {

            x.belongsTo(Arrays.asList(1, 2, 3, 4));

            x.is(even);

        });

// duplicated = {4,8}

```

### Further reading

* [Set-builder notation.](https://en.wikipedia.org/wiki/Set-builder_notation)

* [How are programming languages supporting this today?](https://en.wikipedia.org/wiki/Comparison_of_programming_languages_(list_comprehension))

* [Haskell's list comprehension](http://learnyouahaskell.com/starting-out#im-a-list-comprehension)

### License

MIT